Tachometer in 1978 930 not working anymore
 

Hi

I have a 1978 930 were the tachometer suddenly stopped working.
Boost gauge still working, but tachometer shows 0 all the time.

I am not sure were the wire for the tachometer goes, so if anyone have a wire diagram it would be good :)
I guess I have to check the tachometer it self, and also the wire/signal.

Is the signal going thru the ignition box? I have now a MSD ignition, and have seen that people having trouble with signal after installation, but this box has been in the car for 2 years now.

I would be very thankful if someone could give me some tip to fix this :)
Have also read something about a bad alternator could give this fault?
Only problem i can se so fare is the tachometer. Everything else works perfect.

Sorry for the bad english, but hopefully you will understand what i mean :)

Best Regards
Tor Erik

A bad alternator can kill the tach. But usually you get a warning - the tach starts bouncing around - voltage spikes from regulator in bad alternator. You can check alternator with voltage measure at battery while engine running thru to say 2500 rpm.
The tach runs off the bk/vi wire - which feeds into the TD terminal on back of tach. This wire comes direct from CDI . So direct from CDI (thru 14 pin connector on relay panel) to TD on tach.
Make sure you have 12 v at tach also. And an earth. If you loose either, tach no go also.
Alan