im having trouble with my tach. i picked this 84 cherokee up and the tach bounces all over. it goes anywhere from 1000-5000 or so. it doesnt ever read steady, its constantly bouncing and twitching. has anyone had a similar problem?

thanks in advance

 

sounds like a loose ground wire

 

where abouts is the ground wire for the tach? or is it a ground wire for the cluster? my speedo does it on occasion also...