Hello all
I have a 1988 911 cabriolet. Tach is not working. I did have an overcharging issue now have replaced the alternator. Tach checked at North Hollywood speedometer works perfect on the bench, [all lights work] ECU was tested on another Porsche, on that car all items worked. I am missing something, any suggestions, or others with a similar problem. .

 

looks like there is a green wire that is connected to the speedometer and is jumped to the tach... check the brown (ground) wire as well.

 

Thanks, Redridge I will check the green and brown. Is the Black velvet on the tach a direct run to coil? This all started after alternator replace from 17 vollt over charge issue. ECU checked on another cart, was ok Just happened right after battery and alternator replacement

 

Black/Violet, goes to the DME... I think that is the signal for the upshift light. It sounds like a bad connection somewhere between the tach gauge and the tach sensor (tachogenerator). Though Im not sure where that is. If the wiring is good, then the sensor is bad.