bigred2171

Just dont know where to start.
whenever headlights are turned on my tach. dies.
as soon lights are off tach comes back to life
thanks all for your help

PorschePhD

My bet is that the alternator is going out or the diodes in the alternator are going out.

Cajun

^^^+1. My tach started acting weird when my battery was beginnning to die...

I would bet either your battery is getting weak, or your alternator is going bad.

Bruce Eyring

Be sure the positive and negative connections to the battery are perfect...especially the negative ground. Even if they look 100%....clean them again and be sure they are light. Try slightly twisting the negative cable on the battery post by hand ..... once or twice....sometimes this will fix ...but still clean and reattach cables to clean posts. If not...my bet is that battery is problem.

bigred2171

Thanks all for your replies.
Could it be that I recently installed one of those kill switch(the one with the turning ****)?
battery is brand new and cables are nice and clean.

JFairman

I've seen stuff like that happen in other cars that use a flexible ribbon like circut board behind the dash to connect everything, and it was a poor ground that was causing instrument problems.
One of the really cool things about 911's is each instument is a seperate unit like a race car and flexible circut boards don't live back there... of course 911's are just detuned race cars with a comfortable interior..

anyway, I'd try removing the tach and checking and cleaning the ground spade terminal along with the other things suggested above.
German cars use brown wires for ground.

It's usually easist to wiggle and pull out the clock (or mechanical boost gauge) first and then reach in and push the others out from behind.

I have one of those chinese made battery disconnect terminals on the battery ground post like you mention too and so far it works well.
They are really cheap $ at Walmart.
I would try removing it too though...