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 appriciated as I may have to go the dealer to fix it soon. (Need the A/C!)
Thanks

 

if you need wiring diagram, you must give me your VIN or chassis number.

 

My car is a 1992 300sd - vin # WDBGB34E8NA071799. I am grateful for any help or suggestions!

 

this makes sense:

the tachometer signal (tn) comes from the base module, and so is the airconditioning system.

on the top of the base module, you will find 4 fuses if you suspect this to be the problem.

the engine speed signal of course comes from the starte ring gear speed signal, then to engine diesel system control unit, then to base module, then to the instrument cluster.

follow that line... you won't miss it.

[IMG]local://upfiles/1/CFF693163E574BA8B904AA13E545912B.jpg[/IMG]

 

Sleepwalker:

Thanks again. I am going to try to trace the problem this morning. I'll let you know how I make out.
Tim

 

My mechanic is repacing the engine speed sensor on MOnday, as this effects both the tach and a/c. I'll let you know if it fixes the problem.