tired tachometer

I have a 93 BPA. The tachometer in the instrument cluster works at times, then stops working, then back and forth, and it doesn't matter what the weather is. If I smack the top of the dash board when it stops, it works for a little while, but it mostly does what it wants. :screwy:
I assume that it is electronically controlled, and I am at a loss on how to fix it....if it is at all possible? Can anyone give me advise on what I can try to fix this problem....and maybe a picture or 2 to go with it?
Thanks alot everyone!!

I know the tach lead down by the ignition control module is white, but I'm not really sure what color it is up behind the gage cluster. This lead seems to be loose up behind the instrument panel. If you can get the instrument panel out, check all of the wiring in the harness behind it to see if anything is poorly connected.

Thanks Loekee75! I will probably take a few pictures when I take it apart and post them here if I get the problem fixed.

:bigthumb: