Electrical equipment and instruments (54)

My Mercedes-Benz SLK350, another nice car, along the Eskilstuna å

My Mercedes-Benz SLK350, another nice car, along the Eskilstuna å. Maybe you recognize the background from the old pictures of my 219, e.g. in the article Some more....

This group, 54, is quite extensive so it's divided into several parts which can be found and reached via the sub menus, under "Electrical equipment and instruments". Enjoy everything!

Other electricity related articles are Electric system and Electrical equipment, engine.

Battery (54)

Bosch Classic Battery, could have fit my Mercedes-Benz 219 perfectly

Bosch Classic Battery, © Robert Bosch GmbH, should have fit my Ponton perfectly. But it doesn't. Not their fault though... 

Battery brackets and fixing frame

I thought this would be pretty straight forward. Clean the battery frame and fix new battery floor brackets as replacements for the old, rusty one. Of course it wasn't…

  • Old Ponton battery floor brackets
  • Brackets in place together with the W105 dividing wall in the engine compartment
  • Measuring the old battery brackets, 174mm
  • Assuring that the wall is straight with a steel ruler

While fixing frame and brackets, I double checked the measurements to find out what battery would fit. A nice-looking Bosch old style battery was the goal. To my surprise it wouldn't fit. My data card shows that the car came with a normal Varta battery. The measurements of it I haven't been able to verify. With the help of Bosch Automotive Tradition (who spent a lot, lot of time on this matter together with me! Thanks a lot!!) I got hold of their old data sheets for the 219 (specifically for model year 56 – 59). According to that their standard battery was named BA/12/56/2 (also known as 0 180 055 611) and has the following dimensions:

  • Length: 311 mm (incl 5mm spare between rim and battery housing to the left and the right)
  • Width (=depth): 182 mm (according to Bosch no spare between rim and housing)
  • Height:  220 mm
  • The old sound dampening, have a cut out for the Ponton battery

With my depth measure this would be a problem. From the front end of the bracket to the dividing wall (the wall between the engine bay and the coupe) I have 174mm and from that you have to remove another +2mm for cardboard of the sound dampening (note photo above of the sound dampening board where there actually is no sound dampening material right behind the battery). I miss at least 10mm for being able to buy the Bosch "correct" battery!

My father has done nothing in this area. Me however, have had some of the lower parts of the dividing wall replaced. Moisture (and/or battery acid?) in the sound dampening had caused severe rust. One could of course suspect that when the welder redid these parts, something went wrong. On the other hand, my old bracket fits perfectly, the wall is completely straight and everything else fits and seems to be ok. You can see the last picture in the first group above that the wall is perfectly straight along the steel ruler. Remember, only parts of it was replaced so I can check that. From a Mercedes-Benz 220S -59 owner I got measurements that perfectly fits this Bosch battery. His battery shelf was not only deeper but also looked slightly different around the right bracket.

What I know is that my car, an early (February) 1957, seems to differ in a number of detail designs, compared to other, especially later, cars. As usual, neither Mercedes-Benz in Sweden nor MB Classic Centre in Germany have been able to help me out. According to them there is only one design of the battery shelf for the Pontons...

Well, there are other batteries out there so I will fix it but it is a bit annoying and strange.

  • Here is the drawing for my new battery brackets
  • The new brackets, with the right one aallowing for width adjustment

I had new brackets made. The right one I "designed" so that it would allow for (minor) adjustment to different battery lengths. Unfortunately, the finish of the job was not the best but I take another short cut here since it only concerns the screw holes (!) and they won't be visible.

  • The old battery fixing frame
  • The newly restored Ponton battery fixing frame with tightening screws

And then we have the before and after pictures of the battery fixing frame.

Instruments and switches (54)

Drawing of MB 219 instrument panel, © Daimler AG

Drawing of the instrument panel for the Mercedes-Benz type 219, © Daimler AG

Combi instrument

Disassembly and restoration of the individual parts

The instruments were in a decent shape but as usual I tried to aim for a “like-new” state with all parts of the instrument cluster or as it is called in Mercedes Ponton-language, combi instrument.

First the front of the cluster was removed from the cluster itself. As you can see in the third picture above, the old grey vinyl was dirty, discolored and in an overall bad shape, both from usage and also due to the storage and handling during the restoration.

  • Ponton combi instrument front is unscrewed
  • Rear side of combi instrument front
  • Front side of combi instrument front

After that the chrome frame went off. Underneath it you have three sealings. After that you peel off the instrument glass. As you can see there are a couple of rubber sealings glued into the frame, probably for vibration dampening for the glass. From Ka-Ja TachodienstKa-Ja Tachodienst I got a new set of rubber.

Since the chrome frame had some pits and cuts it was sent for re-chroming together with the clock’s frame. 

  • Chrome frame off, sealing is behind
  • Peeling off the instrument glass of a Mercedes-Benz 219 combi instrument
  • Rear side of Ponton instrument cluster chrome frame with rubber sealing, probably vibration dampening
  • Where the rubber sealing in the chrome frame was glued

The we have a couple of pictures that show how the vinyl is glued onto the frame.

  • Top side of front
  • Bottom of front
  • Right side of front
  • Left side of front
  • Rear side of front

For protection and a clean surface for the new Roser red vinyl, the front was brushed and repainted. As you may understand that paint will not be visible. 

  • Front cleaned and brushed
  • Combi instrument front being painted
  • Combi instrument front painted,ready for new roser red vinyl

When it comes to the disassembly of the base plate, be careful when you remove the foam rubber profile that is glued onto it and which seals against the front of the combi instrument. Don't "drag" it off the plate because then it will end up like mine, two sizes too big (see below) or you may brake it. I haven't been able to find a replacement. Next step was to remove the old lamps, cables and different instruments from the base plate.

  • Disassembly of combi instrument base, its instrument, lamps, cables etc
  • Disassembly of combi instrument base, its instrument, lamps, cables etc
  • Disassembly of combi instrument base, its instrument, lamps, cables etc
  • Disassembly of combi instrument base, its instrument, lamps, cables etc
  • Disassembly of combi instrument base, its instrument, lamps, cables etc

The front of a Mercedes-Benz 219 Ponton combi instrument and the parts that were restored by Ka-Ja Tachodienst

The front and the parts that were restored by Ka-Ja Tachodienst

The first picture below shows the old water temperature gauge and sensor and the second the restored. Ka-Ja Tachodienst did a complete overhaul incl replacing the capillary tube and tested the complete unit.

  • Unrestored water temperatur gauge and capilar tube
  • Restored and tested Ponton water temperatur gauge and new capilar tube

The first two pictures show you the original status and the third the restored and tested oil pressure gauge.

  • Unrestored oil pressure gauge
  • Unrestored oil pressure gauge
  • Restored and tested oil pressure gauge

The first and the sixth picture show the disassembly of the speedometers base plates. The fifth shows the wear on the gearwheels and finally you have the repaired and tested speedometer.

  • First part of removing speedometer from base
  • Speedometer
  • Speedometer
  • Speedometer
  • Wear on MB219 speedometer
  • Second part of removing speedometer from base
  • Repaired and tested Ponton speedometer

The Ponton fuel gauge consists of two parts, the fuel gauge itself as well as the fuel sending unit that is mounted in the tank. Both units were restored and tested together.

  • Original fuel gauge and fuel sending unit
  • Original fuel sending unit
  • Restored and tested Ponton fuel gauge
  • Restored and tested Ponton fuel sending unit
  • Restored and tested Ponton fuel sending unit
  • Restored and tested Ponton fuel sending unit

Finally, we have the lamp cluster in the Ponton combi instrument containing control lights for the blinker, choke control and main beam light. This one I handled myself. First the cluster was desoldered from the base plate. Then the front was removed and the small net and the colored plastic tabs were carefully cleaned. New lamps were installed, Osram 3796 12V 2W. Done!

  • Base and lamp cluster in the Ponton combi instrument containing control lights for the blinker, choke control and upper beam light
  • Removal of Ponton lamp cluster
  • Removal of lamp cluster
  • Removed lamp cluster
  • Front, net, plastic tabs and base of Ponton lamp cluster cleaned
  • Ponton lamp cluster with new bulbs, Osram 3796 12V 2W

Assembly

First the lamp cluster was mounted and its related cables soldered. Then I started to mount the different instruments. See to that you align them correctly. This can be done in two ways; when you mount the instruments onto the base plate and/or by carefully loosening the screws that holds the instruments' fronts.

As mentioned above, be careful when you remove the foam rubber profile that is glued onto the base plate. Don't "drag" it off the plate because then it will end up like mine, two sizes too big (see picture). It was a bit problematic to "compress" the profile and glue it back. Doesn't look perfect but it seals against the front of the combi instrument as it should.

  • Lamp cluster soldered
  • Water temperature and oil pressure gauges mounted
  • Water temperature and oil pressure gauges mounted and aligned
  • Fuel gauge and lamp cluster mounted
  • Fuel gauge and lamp cluster mounted and aligned
  • Over-sized foam rubber profile for Ponton combi instrument
  • Foam rubber profile glued to Mercedes-Benz Ponton combi instrument base plate

Testing the fuel gauge

After the assembly of the instrument cluster I decided to test the fuel gauge and the corresponding fuel sending unit (or "Electric transmitter for fuel indication" as it is called in the spare parts catalog). The workshop manual gives you all the necessary values for this test. Would be a walk in a part. Right…

Excerpts from Mercedes-Benz Ponton Workshop manual regarding testing of fuel gauge

Excerpts from Mercedes-Benz Ponton Workshop manual regarding testing of fuel gauge

First, I tested the fuel sending unit. I choose to test if it gave the correct Ohm-values for full, half full and almost empty tank. With the battery and instrument cluster disconnected you measure the resistance between ground and the contact labeled “G” (in the pictures below it looks as if battery and instrument is connected, that is not the case). I mounted the unit in a stand for a micrometer and positioned it according to the instructions in the workshop manual. With the help of two pieces of cardboard, cut to prescribed height for "full" and "half full", and a good-looking nut, with the height of an "almost empty" tank, placed under the plastic float I could measure the resistance given by the unit’s internal coil.

  • Setting up the test stand for a Ponton fuel sending unit
  • Testing the fuel sending unit for full tank
  • Testing the Ponton fuel sending unit for half tank

Problem with the "evil eye" and my tries to remedy it

The Ohm-measurements were on the spot. Next, I connected the fuel sending unit to the fuel gauge’s via the instrument cluster’s cable harness. The fuel gauge showed the correct amount of “fuel” as well. Last test was the “evil eye”, the red light that indicates that you have very little fuel left. It turned on as it should, after a couple of minutes. But then it went out after 4-7 minutes. That’s not correct. The “evil eye” should shine until you shut the car off or fill the tank (over the 5-6l threshold). I tried to make a new test but that didn’t work until I had waited at least 20 minutes. Did the bi-metal contact that controls the “evil eye” overheat in any way?

So, I took the gauge out of the cluster and tested it again. The light turned on as it should and didn’t go out even after another test or two. Hmmm… Where could the problem lie? Did it overheat due to bad air circulation when mounted in the cluster? Sounded odd, how would it then be when it was put into the car?! Bad solder joints or even a bad cable harness (which still had the original cables from -57)?

  • Testing the Ponton fuel gauge for full tank
  • Testing the Ponton fuel gauge for half tank
  • Testing the Ponton fuel gauge for almost empty tank
  • Testing that the Pontons fuel reserve lamp works

I went for the two latter possible causes and managed to find new wires with the correct, original color coding in Germany. Delivery took 4w as usual when Deutsche Bundespost and PostNord in Sweden are involved. You cannot stress in the restoration business.

I desoldered the wires from the connections in the base plate of the cluster and dragged them out. Having taken the protective tube off the wires I noticed that the ground wire was stripped from 5cm after the contact. Why it had been stripped I was never able to figure out. I thought that this may had been the cause, some sort of short circuit, but unfortunately, as you will see below, that was not the case.

  • The length of a Ponton instrument cluster cable harness
  • The individual wires in the cable harenss. Note the stripped ground cable
  • New, correctly color coded wires and protective tubes for Ponton instrument cable harness

Drawing of Mercedes Ponton instrument cluster cable harness

Drawing of the instrument cluster cable harness

I started the soldering with the joints on the baseplate of the instrument cluster since I have had problems getting nice solder joints when the wires were cut to length. If I would do this work again, I would however start at the socket end.

  • The wires in the base plate soldered
  • The soldered wires with their protective tubes

Layout drawing of Mercedes Ponton instrument cluster

Layout drawing of the instrument cluster

While making the new harness I also found out that the original solder joints on the socket were not only formed like cubes, but also looked frosted/crystalline. Were they so called “disturbed joints” or had they used another solder? I never found out. I used a large soldering iron directly on the wires to be able to get them out quickly without melting the “solder cubes”. The solder that got stuck on the wires did also lock funny/strange…

In two last pictures below, you can see that the solder joints in the female contact on the main cable harness are not formed like cubes, but cylinders!

  • Socket for Ponton instrument cluster cable harness draged out, first side
  • Socket for Ponton instrument cluster cable harness draged out, second side
  • Rear view of Mercedes 219 instrument cable harness socket and solder joints, first side
  • Rear view of Mercedes 219 instrument cable harness socket and solder joints, second side
  • Old solder joints on wires for instrument cluster
  • Socket on Mercedes Ponton main cable harness, first side
  • Socket on Mercedes Ponton main cable harness, second side

To get the new wires soldered deeply enough into the cubes on the socket I drilled a hole in each cube. The wires were then soldered one by one, being hold steady by a “third hand” whose jaws were covered with tape to protect the cable insulation.

As you may understand it was a bit tricky to solder these wires with such a short length sticking out below the protective tube. So, start your soldering here…

Even though I checked everything 10 times I of course managed to mix two wires up. I noticed it just before I was going to tell my wife that the cluster was finally done. The wire order in the pictures below are however the correct one.

  • Holes drilled in old solder joints
  • Soldering new wires in Mercedes-Benz 219 instrument cluster socket with the help of a third hand
  • Rear view of Mercedes 219 instrument cable harness socket with new wires and solder joints, first side
  • Rear view of Mercedes 219 instrument cable harness socket with new wires and solder joints, first side

Layout of Mercedes Ponton instrument cluster socket wiring

Layout of the instrument cluster socket wiring

With the new cable harness in place I happily hooked everything up for new tests. Sadly, it didn’t work now either. After further research I was sure the bimetal overheated in some way and turned the “evil eye” out prematurely. Looking closer at the contact I realized that the paper wrapping on of the coils seemed to have slid down. You can see this in the fourth picture. In the fifth picture you can see the paper that protects the coil and how close it is to the other part of the contact.

Firstly, one paper wrapping had slid down. Secondly, the wrapping had started to loosen up, the old glue probably didn’t hold any longer. I suspect that when the coil got hot it, together with the wrapping, expanded. And since the distance between the paper and the other part of the contact is so small it disengaged the contact and the “evil eye” turned out prematurely.

Even more problems before the solution

First, I tightened the wrapping of the contact part that is closest to the gauge’s base plate. With a pincette and glue that was not difficult. Then I tried to push the other coil with wrapping upwards and then tighten its wrapping. I almost managed to do that, but unfortunately, I broke the tiny coil wire on the same time. After that the “evil eye” didn’t turn out after a couple of minutes so from that perspective the gauge worked. But it turned on after only 20 seconds of “empty tank”.

I never found a source for this tine wire. It’s said to have very specific specifications in terms of resistance and only ~5/100 mm thick. E.g. has the fuel sending unit of a /8 (W114/115) a wire that has a specific resistance of 292 Ohm/m. If the Ponton fuel gauge has the same wire I was never able to figure out. I got a source for the wire, VDO, but they turned my request down. Let me know if you know the specifications and/or know where to get it.

When you look at the pictures below, remember that the gauge and the cluster are not “laying”, they are “standing up” ;-).

  • Bottom view of Ponton fuel gauge
  • Top view of Ponton fuel gauge
  • Angle top view of Ponton fuel gauge
  • Protective paper on MB 219 fuel gauge bi-metal contact which has slid down and risks breaking the contact when warm
  • Protective paper on MB 219 fuel gauge bi-metal contact which has slid down and risks breaking the contact when warm

Below you can see the wiring diagram of the “evil eye”, the fuel reserve lamp. I have not opened up the fuel gauge and studied the components and wiring of the needle so that is not depicted here.

Electrical scheme of Mercedes Ponton fuel gauge and its fuel reserve lamp with the bi-metal contact

Electrical scheme of the fuel gauge and its fuel reserve lamp with the bi-metal contact

Maybe I’ll continue the search for the wire and repair my old gauge just for the fun of it. But to get some progress with the restoration I decided to search for a new gauge. Karasch could quickly provide me with a NOS fuel gauge.

  • New old stock Mercedes Ponton fuel gauge in box
  • New old stock Mercedes Ponton fuel gauge in box
  • Front view of Ponton fuel gauge
  • Right side view of MB 219 fuel gauge
  • Top view of new Mercedes fuel gauge
  • Left side view of MB 219 fuel gauge
  • View of bottom om new W105 fuel gauge
  • Bi-metal contact on Ponton fuel gauge
  • Bi-metal contact on Mercedes-Benz 219 fuel gauge

Final assembly

With the new gauge in place everything worked as it should. Now it was time to finalize the front plate. Based on the old vinyl I cut new pieces of 1079 “Roser red” vinyl and glued them onto the front plate. Most of the vinyl on top of the front plate will be covered by the wood that lays on top of the dash, just behind the wind screen. The frame was re-chromed, and I got new 2mm foam rubber from Ka-Ja Tachodienst to place between the frame and the glass pieces. The assembly was easy. Insert the tabs of the frame into their holes in the front plate. Carefully, but firmly, press the frame into a tight position and then turn the tabs 90 degrees. Done.

  • Old, lower part of vinyl for Ponton instrument cluster
  • Old, upper part of vinyl for Ponton instrument cluster
  • Foam rubber for holding glas in Mercedes instrument cluster
  • All parts for the Mercedes instrument cluster, ready for assembly
  • Glass in place on Mercedes instrument cluster front plate
  • Restored Ponton instrument cluster front plate assembled

Then you assemble the base plate with all its instruments with the front plate, taking care of getting the “big” foam rubber in place. Carefully, but firmly, press the base plate and front plate together and tighten the screws on the backside.

The cluster is beautiful and knowing that everything is 100% OK makes it even more beautiful. Now it’s just a matter of making some progress with the rest of the restoration so that I can put it where it belongs, in the dash.

Restored Mercedes-Benz 219 Ponton instrument cluster

The completely restored instrument cluster

A word on the speedometer

I got a question from one of my visitors to the site, if my speedometer was original. Since the part number stamped on it is 121 542 03 01 it point towards that it comes from one of the 4-cylinder Pontons.

Mercedes-Benz 219 Ponton speedometer with its combi-instrument article number stamped on it

The speedometer with its combi-instrument article number stamped on it

That question was interesting. Never thought about it since the speedometer to my knowledge is the original one. I know that for sure (well at least to 99%) since my father and I often discussed how many kilometers the car actually has been driven. I still not know for sure since tere is a gap in its records even though he had it from new. But not one time during these discussions he said that it had been replaced.

Looking in the spare parts list that article number actually refers to the whole combi instrument, not only the speedometer, and then for cars up to chassis number 750 3492. Mine has 750 0912 so that's the combi instrument I should have. Later 219s (W105) has an article number starting with 105. If I understand the list correct the spare parts number for the actual speedometer is however 001 542 43 06.

The clock

This is a mechanical clock. A lot of people have recommended me to replace it with the later, electrical version. For me that’s a big No. Winding the clock is for me something special; you close the door, settle in and wind the clock as a preparation for the trip. And there is nothing more relaxing than coming home with the car, parking it in the garage and listen to the clock’s tick-tack for a couple of minutes. Winds me down…

The cover glass of the clock was broken and the small rubber sealing that sits on the shaft where it goes through the glass was old and dry. New was ordered from Ka-Ja TachodienstKa-Ja Tachodienst together with the new rubber sealing for the shaft. The chrome frame was taken off. On the rear-side there was rubber melted (?) into it, I assume for vibration dampening. After pealing it off the frame was sent for re-chroming since my father have had it off for servicing of the clock and therefore it was slightly bent and damaged.

  • Ponton wind-up clock with broken glass
  • New glass and rubber sealing
  • Chrome frame taken off
  • Rubber between clock housing and frame

I also wanted to have the clock mechanism gone through. Hence, I had a watchmaker go through it. There was nothing to repair or replace except dirt and old, hardened oil and grease. That was removed and the mechanism re-oiled.

  • The clock was gone through, old hardened oil, grease and dirt removed and new oil put in place, first picture
  • The clock was gone through, old hardened oil, grease and dirt removed and new oil put in place, second picture
  • The clock was gone through, old hardened oil, grease and dirt removed and new oil put in place, third picture
  • The clock was gone through, old hardened oil, grease and dirt removed and new oil put in place, fourth picture

With everything gone through and frame re-chromed the assembly was easy and the result perfect.

  • All parts for Ponton W105 manual clock ready for assembly
  • Restored Ponton W105 manual clock assembled

Cables

New Mercedes-Benz Ponton cable harness

A new Mercedes-Benz Ponton cable harness

Above you can see parts of the new cable harness (some parts, like the rear branch, are already installed in the car). This harness was ordered from Krieg Kabelbäume in Germany. It looks exactly as the original Mercedes Ponton cable harness; every cable is cut to correct length, has correct color coding and is provided with correct terminals. When you order it you can even add new cables as per request. In my case I added cables for the radio, for glove as well as engine compartment light, extra cables for the trailer hook I have - and may install - and also a hazard light function including the extra switch. Verrry neat. 

Before installing the harness I needed to perform a couple of things:

  1. Understand and verify all cables and their connections, that the harness was correctly built
  2. Clean up, reconnect and verify the new cable harness to the fuse box and to three cable sockets, for the tail light harness, for the steering spindle cable and for the heater blower cables
  3. Solder and verify the socket on the main cable harness for the instrument cluster

I suppose the galleries below are self explanatory. The first shows the fuse box and the different sockets. The screws in these sockets where still in very good shape and hence not plated (the screws in the steering cable socket is brass and hence not plated).

  • The old cable harness
  • The old harness' connection to the fuse box
  • The first, new cables having been attached to the fuse box
  • Checking what cables to connect where on the Mercedes Ponton fuse box
  • All cables connected to the Ponton fuse box
  • Mercedes Benz 219 Ponton fuse box restored
  • The old cables on the tail light harness socket, found under the Mercedes Ponton's dash
  • The old cables on the connector for the steering cables
  • The old cables on the connector for the steering cables of the MB 219
  • Restored sockets for the Mercedes Ponton main cable harness

The second gallery shows the resoldering of the main cable harness' instrument cluster socket. Took some time verify all the connections on the main cable harness as well as its connection to the tail light harness. For the soldering of the socket, please also see Instruments and switches.

  • Checking the layout of the main cable harness' instrument cluster socket carefully on a Mercedes W105 Ponton
  • The layout of the main cable harness' instrument cluster socket on a Mercedes Ponton
  • Having drilled holes for the new wires in the MB 219 main cable harness' instrument cluster socket
  • Re-soldered Mercedes Ponton type 219 main cable harness instrument cluster socket
  • The new main cable harness checked and complete

It can be noted that the tail light harness, a bit more simple in its layout than the main cable harness, was already mounted in the car.

Electrical equipment and instruments (54)

Dual tone horns

Dismantling and repairing the dual tone horns are not especially difficult. A lot of information can be found on the internet but often hidden from google in different oldtimer forums for e.g. Mercedes, Volkswagen and Porsche models from the fifties. Some people tries with the "there is  o n e  thing that you need to do right and it's very difficult. I won't say what but I can restore the horns for you for a fair price". That is b-llsh-t. I've seen restorations with step-by-step instructions where people have turned more or less a pile of rust into very good looking and functioning horns. Have e.g. a look in the "Early Early 911 registerEarly Early 911 register" and "Pagodentreff.dePagodentreff.de" (in German) for reference material. I don't want to copy and paste the instructions due to their copyright. The only thing that may be a bit problematic is to adjust the frequency of the signal so that it sounds as it should.

Mercedes Ponton Bosch HO/FSA 12 bass and high tone horn restored

Bosch HO/FSA 12 bass and high tone horn restored

I can again be very thankful to my father who cared for the car. For me it was almost just to take them apart, clean and paint everything and then test.

I must again highlight the importance of being meticulous when you take them apart; take pictures, make markings, measure everything and see to that you know in what order everything goes. I wasn't, so I had a couple of hours of trial and error until I got them working...

The first problem was that I had taken one of the horns apart long time ago and hadn't made the temporary assembly correctly. The second problem appeared when I started this restoration work; I did both at the same time and hence mixed some things and pictures up.

Note; in the photos below I will mix pictures from both the horns. "F150" is the rear bass horn mounted on the left wheel arch, behind the radiator, and "F151" is the high tune horn mounted in front of the radiator. The difference on the outside should be obvious and they are identical on the inside except the settings of the tuning screw of the frequency. Each has its unique frequency (stamped on the central plates!) so that the two tones match each other and give them and your Ponton its unique horn sound. I measured the tuning screw settings and re-used those. Seems to work…

If you need to adjust I assume you will need a tool for measuring frequency. The long tuning screw in the centre adjusts frequency and the adjusting screw on the back of the housing adjusts the function of the contact. As I've understand it, it is normally the long pin in the center that you make most of your adjustments with.

  • The high tune Ponton horn, mounted in front of the radiator, before restoration
  • Rear side of the high tune horn

"Before" first. "After" later…

  • Old, black plated screws for the Ponton horn cover
  • Cover taken off the high tune horn
  • Mercedes-Benz 219 vibration plate and casing separated
  • Rear side of vibration plate
  • Paper gasket between plate and casing
  • Vibration plate again
  • Rear side of casing with electrical connections
  • Spacer collar in a dual tone Ponton horn

Notes; In the first picture you can see the screws holding the cover, the were black plated. In the seventh picture I've written "black?" close to the cable connector screws M4x6. Forget that. They should all be white "cadmium". 

The tuning screw for the rear horn was protruding ~0,6mm and for the front horn ~1,1mm.

  • A drawing for making new paper gaskets for the HO/FSA 12 Ponton dual tone horns
  • New paper gaskets

Then it was time to make four new "petrol-oil-water-ect"-resistant paper gaskets. I covered them with a thin layer of Vaseline to make them easier to hold in place while doing the assembly.

  • Cover, vibration plate and bracket for high tune Ponton HO/FSA 12 horn
  • Cover, vibration plate and bracket for bass tune Ponton HO/FSA 12 horn
  • Rear side of casing, sloted screw that allows adjustment and removal of the contact support bar.
  • Rear side of casing, other side though..
  • Cleaning up the interior, the electromagnet, contacts and terminals

Then I did the sandblasting, grinding and cleaning. First you see the high tone horn and then in the second picture the bass tone horn. In the third picture where you have the rear side of a casing you see a slotted screw that allows one type of adjustment (don't know which actually, didn't try it) and removal of the contact support bar. 

  • Preparing for painting the casing
  • The casings with a layer of primer
  • Brackets, cover and parts of the vibration disks primed
  • All parts black painted (note that there are other parts there, that do not belong to the horns)

You could of course remove all the electrical wiring and rubber gaskets but I decided just to protect them before the paint. First one or two layers of primer and then glossy black on the top. In the last picture you can see all parts having been painted black, but note that there are also some parts that do not belong to the horns!

  • All parts for the rear side of the casing of the HO/FSA 12 Ponton horn ready for assembly
  • Rear side of horn casing assembled, note that screw and nuts should be black plated

Then the housing was assembled in terms of bracket and electrical connections. The Bakelite was cleaned white spirit, polished with Greygate's "Paste Polishing No 5" and protected with bee wax all according to a Bakelite restoration site (for restoring old phones). There are many ways to restore Bakelite. I did it this way… Maybe a layer of lacquer would have been more protective in this environment than bee wax, but... Note, that the screw and the nuts in the last picture are not black plated as they should and later would be!

  • The two Bosch central plates for the Ponton dual tone horns

The two Bosch central plates, were cleaned and covered with a couple of layers of clear lacquer. Be careful, the text on the plates is fragile and doesn't stand too much solvent.

  • Contacts and capacitor
  • Assembly order of a Ponton dual horn from Bosch
  • Home made aligning tool for the parts in the dual tone horn

In the first photo you can see contacts that you may have to clean. The second photo shows the correct order for the rear horn. In the front horn you don't have the Bosch plate on the central tuning screw, but the order of the washers in front of the large disc is the same. The third photo shows my "third hand" while assembling all the parts.

My Mercedes-Benz 180K, W203

My Mercedes-Benz 180K, W203

Put a little amount of grease on the part of the central tuning screw that goes into the anchor and magnet. Position the tuning screw so that the bevel in its "screw" is fixed by the splines in the central pin so that you can adjust the horn by carefully turning the pin. Be careful, if you unscrew the "screw" too much it will lose the connection to the pin and get stuck.

  • Testing the dual tone horns. Note that the sound is high!

Finally I tested the horns, connected according to the electrical diagram in the workshop manual. Doing this in the basement, even my neighbors wondered what was going on. Warn the family and wear ear protection!

  • Bosch HO/FSA 12 Ponton bass tone horn
  • Bosch HO/FSA 12 Ponton high tone horn

Tada, the horns ready for usage! First picture shows the bass tone horn (mounted behind the radiator) and the second the high tone horn (mounted in front of the radiator). However, I wouldn't be surprised if the screws holding the cover were painted together with the complete, assembled horn and not only black plated as mine are. Well, easily adjusted if that's the case. But black they should be.