I started having a weird issue with the temp. gauge today. I went to start the car and as soon as i turned the switch over to the Acc position, the temp gauge jumped all the way to the top.

I thought it might because of a loose connection to the coolant temp. sensor that plugs in to the engine below the glowplugs ( between GP 2 and 3 ) . I did some research and it turns out that this supposedly is the sensor that connects to the gauge in the instrument cluster. SO i unplugged it...nothing. I unplugged the other three sensors that i know of....nothing.
This lead me to believe that the single wire coming in from the sensor must be getting grounded some where , making the gauge jump all the way to the top. I start wiggling cables coming in around the battery box and then closer to the climate control unit. Just as a shot in the dark, i disconnect the right connector on the climate control unit and bam...the needle returns to the normal position, displaying 80 .
I plug the CCU connector back in and it jumps back all the way to the top.
i thought the temp. gauge was independent of all the other units in the car, as in the CCU is supposed to take its readings form the ambient , evap and a separate coolant temp sensor for its functions.

Any ideas as to what might be the culprit . Where should i begin checking this out ? I have the dash apart for re-covering and was about to put it back in today but for this silly little problem. I had issues with CCU before and i was hoping that re-soldering weak connections and the slightly burned part on the board fixed it...maybe not.

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1987 190D 2.5 Non-Turbo , automatic
Currently fixing : diagnosing vacuum functions,
, fuel leak at injectors, Dash Re-covering , speaker replacement with aftermarket amp and new wiring, generic keyless entry system .

Future projects :, antenna , Transmission modulator pressure adjustment or replacement... more to come...

Fixed : Windows, Ground wiring cleaning, random transmission kick-downs.