97 Passat Temp Gauge Problem

I have a 97 VW Passat GLX Wagon and the temp gauge doesn't work. My mechanic said the problem was a bad temp gauge. I have put in 2 different (used) instrument clusters (because you can't buy just the temp gauge by itself) and the temp gauges on both of the "new" instrument clusters didn't work either. My mechanic checked it again and still says the problem is a bad temp gauge, even the 2 "new" ones. He checked the temp sending unit and said it was good. Any ideas?

I know the B3 Passats had terrible problems with the electrical connector to the instrument cluster, not sure if it's as common on the B4's. With the cluster loose try jiggling and twisting the electrical connector & see if the gauge will work at times.

I just tried wiggling all the wires (with the engine running) and nothing happened. I forgot to mention in my first post that the needle moves ever so slightly to the first white line on the gauge. If you're not watching it closely, you won't see it move. I have a feeling the problem is in the wiring but I don't know how to check the wiring. I have a voltmeter but the connectors/leads are too big to fit inside the wiring harness connector's holes. :screwy:

After reading some other posts, I am now wondering if maybe my problem could be in the voltage regulator. My front power windows will go down with the switches but not up. To get them up I have to put the key in the door and hold it in the "lock" position and wait for the windows to go up. Also, last Fall, my heater core blew and I had to replace it. Could some water maybe have gotten into the wiring??? I am totally guessing at all this so any input is appreciated. Nothing has been the same since my heater core blew.