I swaped the cluster and my dash almost a year ago from 88/89 to 90/91 standard, everything was fine, untill one time in the rain I got wheelhop and never been right since.

If I dont turn anything on, the guages seem fine, if I turn my lights on, and then throw a blinker on, the Tach will start jumping, and if I turn my highbeams on it becomes even worse (jumping wise).

I'm pretty sure its a lose ground somewhere, but I'd be damned if I remembered where the ground points are.

Any clues suggestions?

At a stop its usually fine, but not always, during movement, with highbeams and hazards on my tach will jump as much as 7K up and back.

 

The tachometer runs off the dizzy. Replace it with a known one because there might be a loose connection in it.

 

Battery to tranny, valve cover to frame, and there is one on the thermostat housing.

 

So either one of those would mess with my tach?

I'll pay more attention but im sure its my temp and my fuel gauage too that go hay wire.

And im still not sure why turning on turnsignals/high beams effects the amount of paly in guages.