I got the bolt off and will let you know the result in about 10 minutes. (Thanks)

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I got it apart, cleaned it all and put it back together. Unfortunately, it does not seem to have had any effect. The tachometer needle still bounces (sorta in time to the turn signal) and still tries to max out when the horn is sounded.

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Better, Faster, Cheaper, pick two.

Have you cleaned G 101 behind the instrument cluster? If so I would take the cluster out and clean the grounds between the modules (via a screw). Look with a magnifier for bad solder joints and resolder.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Another thing to try with a helper, wiggle the Tach amp and see if the jumping needle stops.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I have not cleaned the ground point behind the instrument cluster. I did run another wire from the back of the instrument cluster to the same metal support as the ground point and secured it with a tight fitting screw into the metal support.

I have also tried another tach amp (one like the original equipment). I put it in, made sure the connection was good and the tach was working, and still had the same result with the turn signal and horn.

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Better, Faster, Cheaper, pick two.

The thing I find most interesting is the fact that the problem only manifests with the turn signal and not the flashers. That is essentially the same circuit, so that doesn't make any sense. I'd suggest pouring over the wiring diagram and see if you can identify something in common with the turn signals and horn that is not associated with the flashers.

Actually, maybe we're looking at the wrong end of things. Maybe there is something wrong in the tach gauge itself - something that makes it hypersensitive to certain fluctuations in voltage or RF or something. Get a tach module at the JY and swap it in, or borrow one from another car and just test it.

Of course you could always swap in an intermediate plate from an '85 and use the '85 tach pickup and module...that's a whole lot of work though!

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

The only place I know of where the turn signal and horn come together is in the steering column. There is a lot of posts about the horn and tachometer, but I didn't find any that included the turn signal.

My next (last) step will be to get another tachometer from the bone-yard and try that. If it doesn't work, I may have to either live with it or live without the tachometer.

Thanks to all who offered help and suggestions. If anything happens to make it work, I will let you know. Or if you think of anything else, please let me know.

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Better, Faster, Cheaper, pick two.

Did you try to wiggle tach amp while needle is bouncing ? Also wiggle cluster connectors (space be tight with oil line connected). If you can get the bounce to stop while wiggling you found the problem area.

Also measure the voltage supply to the cluster, it should be steady and not fluctuate with the turn signal.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

This comes under the "for what it's worth" heading. After taking the steering column apart I have become convinced the problem is NOT in the column or instrument cluster. I say this because the tach seems to work on a voltage reduction. At engine on but not running, the tach gets 12.+ volts. As the engine runs up in rpm, the voltage going to the tach is reduced.

I considered a short in the turn signal indicator lights, but still had the problem with the indicator lights removed from the instrument panel. I tried disconnecting the power supply to each horn for the same reason, no change.

Now on the turn signal, engine running and turn signal on, the voltage goes from 12.+ to 11.5 or so. I didn't measure the full fall in voltage from the horn because I figured the voltage drain would burn out a fuse (8 amp, number 12 I think) like it has in the past.

Maybe I should go buy a new VW....

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Additional FWIW information. I watched closely when the four way flasher is on. It does cause the tach needle to fluctuate, but only a very little. The turn signal causes a major fluctuation, as does the cruise control (not realized before). The horn causes the needle to peg to the right. Also, when the engine is running at higher rpm, the turn signal bounce is not noticeable, but the horn and cruise control bounce is still very obvious.

I checked the battery voltage, engine off is 12.68 and engine running is 14.4, so it seems the battery is good and the alternator is functioning correctly.

I am going to clean the ends of all the fuses, but I don't hold out any hope for a change in the behavior; it just seems like a good maintenance chore.

If anybody has solved the horn to tachometer connection, I would appreciate any advice and or suggestions. (This is annoying me considerably!)

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From the previous posts, it is obvious this has bothered me for quite some time. Now it is fixed. The problem turned out to be the tach amplifier I purchased from someone on this site (I think). It is the one with the blinkin-lights. He makes them, and they generally work quite well, or so the forum indicates. I remember when I first got it, I tried to contact him about it, and I don't remember if he ever replied. I kinda think not, but am definitely not sure. My memory is not what it was 50 or so years ago.

Anyway, after I replaced the socket and all wires the tach amp plugs into, again, I got an old amp that worked sometimes. Plugged it in and wiggled it until the tach worked. I tried the turn signal and got in no bounce. Horn did not cause a bounce either. I then replace the amp with the blinkin-light one and everything returned to the bouncy condition. Turn signal caused the tach to jump in time with the signal, and the horn caused it to peg all the way to the right. Went back to the old style amp, used bubble wrap to hold it in place, and the tach needle is steady as it should be (I now have the problem of the intermittent tachometer again, but I think I will keep that instead of the one that bounces with the turn signal. At least until I can get another tach amp from somewhere.)

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You can get the VDO part from this site. I have one in my signature car and it works fine.

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'83 300D, 126K miles.

Thank you. I will look for it (and the price) as a possible permanent solution.

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The amp with the "blinking light" is my updated, Rev 2 amplifier. Equipped with Power and Pulse LEDs for diagnostics.....

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Bob
'82 300D Petrol B-G Metallic

techguy, that is the one I have. I purchased it and the windshield wiper module from you a couple of years ago. I installed them in my 82 300Dt. The wiper module works fine - as far as I know, but the tach amp is what caused my tach needle to peg to the right when the horn was activated, and twitch (haphazardly) with the turn signal light. Of that I am positive.

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