I did a quick search and didn't find anything about this particular issue, but if I missed a thread about this, please post a link and I'll check it out.
When I picked up my 89 spirit es turbo, I noticed that the tach was inop (would just read mostly random rpms while driving, usually "hovering" at certain spots), and the speedometer needle jumped all over the place when I first started driving the car after it sat for awhile. After about 5 minutes of driving, the speedometer would settle down and seemingly work correctly, but for that first 5 minutes or so, I had no idea how fast I was going.
I ended up picking up a guage cluster from Lengel when he parted out his spirit r/t for a great price, so I stuck that in to see if it solved anything. The tach seems to work perfectly now and the speedometer is better, but it still jumps around from time to time... could this be a ground issue?
I'm planning on re-soldering the contacts on the back of the original cluster, but I'm wondering if there isn't another issue too. I also have a weird blinker thing going on with the driver side blinker in the bumper. It's not blinking even though it lights up and the side marker blinks like a cheap hooker...? Anyway, I'll get to that later, but mentioning it just in case they could be somehow related by ground?!?
Thoughts?