TMWTP

Turned my headlights on while driving, and my tach died instantly. Car continued to drive just fine, headlights worked, all fuses appear to be in good condition. Pulled #18, even though the rest of the gages were working.

Going to pull the tach out to see if it's just a loose connection. My gut tells me there is a ground issue somewhere.

'91 964 turbo, only mods are upgraded projector headlights. Perhaps the ballast isn't grounded properly. If that were the case, I would expect to see a blown fuse.

Any ideas?

TMWTP

Pulled tach, disconnected the cable, plugged it back in, and it appears to be working fine. Go figure.

Will update if it happens again.

bweSteve

that was quick - 12 min between posts

TMWTP

Yeah, I wasn't confident that I'd be able to fix it. As it is, I didn't actually do anything, it just kinda' fixed itself.

TMWTP

Happened again last night. Shut the car off, tach came back when I fired it up again. Also, brake-light circuit had a blown fuse. Not sure if they are related. I'm starting to get the feeling this car needs a new wiring harness.

Metal Guru

I recommend examining everything on the circuit followed by ringing out the harness. Also have a look at the circuit grounding point.

bweSteve

sounds like a grounding issue. vibrations causing variances

Metal Guru

A quick check of the wiring diagram shows that the taillights are not on the same circuit with the instruments.

bweSteve

Paul makes a good point,... which begs a question...

when you say "happened again last night",.. does that mean the tach stopped working at exactly the same instant you turned your headlights on again?

.... or maybe just while you were driving, and possibly hit a bump & the tach stopped working.... ({ just trying to eliminate coincidences })

TMWTP

Nope, happened exactly with the switch, in exactly the same manner as last time. I'm going to go through an the headlight connections and grounds. I recently had the front end resprayed, and I have a feeling the paint thickness at one or more of the ground points might be too thick.

Metal Guru

There's a diagram of all the body grounds in the "Without Guesswork" manual that may be helpful.

TMWTP

Nice! Thanks, never heard of that one. Ordering it now.

heliolps2

Hey There.

How about the headlight switch. I had something similar happen to my 993. That''s where I would start and the grounds behind the fuel gauge, there's about 10 ground wires on one bolt back there. Just a thought

Helio

TMWTP

Thanks for the tip. I'll check that out too.

TMWTP

Update: checked the pertinent grounding locations, all are in great condition. Removed my head lights (HID projectors), put some dielectric grease on the connectors, and ensured they were seated tightly, and secured with some electrical tape. Checked all fuses, and found my frunk/interior lights' fuse was blown. Quick test, and everything works properly. I think the connections for the headlights were loose enough to cause a voltage spike through the ground.