The ground problems I'm having are in the instrument panel. When I used a turn signal, the tachometer needle would dip to 0 every time the turn signal blinked. If I had the headlights or parking lights on, and used a turn signal, the WRONG turn sig indicator on the dash would blink. It seemed that the more electrical load on the lighting system, the worse the problem. I cleaned the grounds at each headlight and one on the mount for the steering column, and the dash is working much better now. The fuel gauge even works now!
After seeing so much improvement from cleaning grounds, I think I need to finish the job and clean ground G201 "behind cluster". After looking at the Service Manual, I think this is the key ground point for the instrument panel and all interior lighting. I'll look for it this evening after work, and let you all know what happens.
As for engine performance and grounds, I can tell you that good grounding is essential. When we bought the GT, we found that almost ALL the grounds to/from the engine had been removed by a previous owner. Here's the thread from that episode: https://www.fiero.nl/forum/Forum2/HTML/052227
[This message has been edited by SC Coupe (edited 08-16-2004).]
