I have posted previously regarding my tachometer occasional dropping to zero. Seems like an electrical glitch because it does not effect the operation of the engine, other than the a/c. I have noticed the air conditioning only works when the tach is functioning. Is their a relay or switch that might be bad? ANy help is appreciated as I may have to go the dealer to fix it soon. (Need the A/C!)
Thanks

Hope I'm wrong but it maybe a wiring harness going bad.

Thta was the dealers first suggestion. The previous owner of this car had two wiring harnesses replaced to try to correct this problem with no improvement. I am hoping there is a relay or sensor that effects both the tach and a/c function. Thanks

It's probably a bad ground. I have the same problem as mine flashes on and off. I am pulling it this wekend to check it out.

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N. Hodges
1994 S350
1987 300 SDL (for sale)

I'm not sure if i am on the right track becuase what model is your car? A similar problem on a 124 would or could be the Kilma relay(just behind the battery) becuase that relay reads speeds from the engine(tach meter) and then from the ac and checks if they are the same, if not the ac compressor cuts out. So either the speed signal from the engine is not 100%(not sure why) or the Kilma could be faulty or loose. This isn't concrete advise but it might help.

My car is a 1992 300SD. I check for a kilma relay. Thanks