i have a 1990 camaro rs. recently my tach began giving me erratic readouts. the needle will not go past 3000 rpm and it bounces around a lot. is there a sensor that registers rpms from the engine to the tach?, and if so, where is it located. i pulled the instrument cluster and it looks more like a printed circuit board form the back. this leads me to believe the problem could also be some sort of electrical malfunction. the engine is a 3.1 6 cyl.