every so often my rev gauge will either drop out so it isnt reading correctly (will say 2000rpm rather than 4000rpm) or will just drop out all together. normally a quick bang on the dials works. but is there any problems commonly known on them?

there are a few things i need to do to mine and with my job going from day break to well after sunset, and my weekends full at the moment sorting my miss's almera gti and a few other cars, its getting quite neglected. just wanna take it apart armed with as much info as possible. lol

Never seen it on a 3 series Volvo, but a 3 series BMW did it and would not run, Just turned over on the starter with the rev counter going mad, problem was a loose +battery connection to the alternator.

the plug on the rear of the revcounter is loose

that can either be a bad contact in the blue print or just the plug itself.
i hade it on my car a while back, after messing around with the plug 50+ times i ended up swapping the blue print, problem solved.

Yeah mine does the same but only when the car hasn't been used for a few days, then it just needs to "warm up" a bit and after a few miles it kicks in and works ok.

I've also noticed sometimes it can't keep up with the rev's from the F7R