If you want to know where my revs are at just wait until I hit the next bump in the road. So when I am switching lanes the reflectors in the road will cause the tach to quickly show where im at for revs than the next set will take it away just as quickly. Its almost like a little game me and my tach play together. Checked all the wiring at the tack and it seems solid, what could be loose? I am getting tired of the game and am ready for a more stable relationship with my tach.

How does the bottom of your relay board look like? Any cracks in the insulation?

I had the same problem when i bought my car. Got a brand new relay board and all was guud ...
Andy

I wouldnt even have thought of that, I will check.

My tach works great...well until I turn on the turn signals...then it fluctuates with the signal lights. When I hit the brakes or turn on the headlights, it shuts off!! Can't figure it out. Who needs a tach anyway?

Try cleaning your fuses.

After that, repair the bad grounds.

The Cap'n