I am having a major electrical issue with the gauge cluster in my 89 IROC. During daytime driving, the tachometer reads approximately 2,000 RPMs too high. I understand that this is a common problem. All other gauges seem to work just fine. When I turn on the right turn signal, the right green blinker lights up solid and does not blink, the tachometer needle bounces around wildly and the oil pressure gauge bounces as well. During nighttime driving, when the headlights are turned on, the tachometer pegs out at 7,000 RPM and the oil pressure and battery voltage gauges both go to zero and remain there until the headlights are turned off. Would it be safe to say that the printed circuit board on the back of the gauge cluster is bad? Could it be a bad headlight switch?

 

I would try checking the ground straps for the headlights forward of where the battery is.
Multiple issues like that are often due to a bad ground connection.

 

I have a 88 iroc and there is no circuit board on the back of the gauges. I had mine out yesterday and there IS a wiring thingie on the back but no components
( resistors, capacitors, etc.). I replaced my temp sending unit and the oil sending unit and now everything works except the factory tach. I solved it with a autometer mounted on the right side of the left side of the dash. I just unplugged the tach wire at the coil and hooked the monster tach there. (White wire)

 

I stand corrected, I was thinking on the back of the white housing, Not the gauge itself, Sorry

 

Yes, it would be called a flex circuit board, components don't define a circuit board.
There is a thread on fixing the tachometer an the later clusters but iirc, it can be used for earlier as well.