Tacky Tach!!
 

Ok. Ive read the arhives, did some searches, feel confident in grounding problems because i had them before, but my problem seems a little different. On my 87 t2 for the majority of the time teh tach and gauges work fine, but occasionly ill start the car and the rpm gauge will jump up to the idle spot around 1000 rpms or so and then immediatly Sink to the bottom. The engine stays running just the gauge stops, wwell i had someone sit in the car and wiggled grounds, moved wires etc... did this repeatdly for about 5 minutes completyly shutting down the car taking the key out and back in. Never came on, i let the car sit for an hour came back, started the car and the rpms gauge worked perfect WHT THE *******

on the back of the gauge cluster is some screws that are used to connect the gauges to the flexible circuit board. Check them for corrosion or bad contacts