Any of you guys have a clue as to what might cause temp gauge to rise to 90C directly

I'v had this problem with my corrado for a long time, but never realy looked into it, but the temp gauge will rise up to about 90C when I turn the ignition - doesn't matter if it's cold or warm.

I'v verified the instrument cluster are working (tested in another car - and another cluster have been tested in the corrado with the same result - rising to 90C).

I'v tried to change out the harness from cluster to fuse box - but nothing changed.

The line from the cluster to the sensor have been measured and seem to be fine.

It will rise up to 90 C even if the sensor is disconnected - so that shouldn't have anything to do with the problem.

I'v tried to compare it a bit to my older Passat VR6 - and what I find differs is following:

reistance between negative battery and pin that goes to sensor (blue/white cable) is 166 on the Corrado and 266 Ohm in the Passat.

The pin that goes to the fan-control unit have aprox 1.6Kohm on the corrado but have about 23-25 (or might have been 30-35 Kohm's) - so quite a bit of difference.

Also when I measure voltage at the sensor pin I get apx 6.3V on the Corrado but almost 10V on the passat. The pin to fan control get aprox 12V on both cars.

Also the ground connection seem to be good.

So I'm starting to run out of ideas on what might be causing this thing to happen.....:(

Video of the cluster can be seen here:

http://s16.photobucket.com/user/Mawrick/m…aa5c11.mp4.html

HELP!

Thanks for the tips - I went thru most of that before - but today I looked back into the bentley and was taking a closer look at the relay panel, turns out a former owner must have put in a relay "72" into slot number 5 - which should contain either a "43" relay or left "open".

I presume this caused it to make a circuit to ground over the coil in the relay - causing a false signal to the needle.....:)

The voltage is now back to roughly 10V at the pin, and all seem to be working

haha, yea was a easy fix, but it was da** hard to track down....lol.......can't see why anyone would put in such a relay there.....lol......would have helped if I *knew* for sure the relay layout though......:)

thnx again!