Turn signals and tach died - coincidence? - PeachParts Mercedes-Benz Forum

VW1300 · #1 06-29-2010, 10:09 PM

Within the last week, the tach on my '85 300D stopped working correctly, and now the turn signal relay seems to be on its way out. Sometimes the signals don't work, sometimes they do. Is this a great coincidence, or is there something I don't know that may tie the two things together?

More info: the turn signals were clicking rather quietly lately, it is conceivable the relay is dying. The tach was working great up until one day it started giving a needle position that was directly related to the position of the accelerator rather than actual engine rpms. For example, if I'm going down the highway - if it works at all - it will show about 800 rpm. If I let my foot off, it drops to zero. Foot back on, back up to 800 rpms. Even more info: about two weeks prior, I had it in the shop for A/C work (don't get me started on that subject), but the mechanic is one of the best in Houston, if he messed something up it was probably not due to incompetence or ignorance. Oh yeah, the tach thing started on the day that the A/C stopped working, presumably due to lost R12 pressure from a leaky compressor. Long story.

Any ideas? I'd like to get my signals working, even though no one else in Houston uses them.

thanks,

#2 06-29-2010, 11:42 PM

Check the fuses; on my 82 the tach, turn signals, and brake lights are on the same fuse. Even if it looks OK, try replacing it.

VW1300 · #3 06-30-2010, 09:51 AM

Well the turn signals worked on the way to work this morning, but still no tach or A/C.

OK, cleaned up the fuses just now. From the Haynes manual, it appears that the turn signal relay is on fuse 2. Hard to say, it doesn't give a diagram for '85 US models. After I cleaned up the fuse, I put it back in and it arced a tiny bit when it touched the contacts. ??? The clock is also on fuse 2, I guess that's where the current is going.

The weird thing is that after the fuse cleanup I tried the A/C and it started to work again. The tach needle moves around but not in direct relation to engine revs. Turn signals seem to work a little faster, though that could be wishful thinking.

Question - until the signals start to fail again, I'll have to let that remain a mystery, but what's the next step to diagnose the tach problem?

thanks,

TX76513 · #4 06-30-2010, 10:00 AM

I am going to step out here a bet you a donut

That it's your ignition switch. If this happens again - with the engine running wiggle your key gently left to right if ac fans, tach, signals start working it's the contacts on your ignition switch (not the tumbler).

.02