1.9TD Golf '93 Temperature Fault

[darowuk]

I have been having a few problems with my Golf. Firstly when I came to start it the other day the glow plug light didn't come on and the car wouldn't start. A mechanic friend of mine came to help and noticed that one of the plug contacts had corroded through, he replaced the plug but in doing so disconnected the coolant temp sensor. The glows then worked okay and the car started, however on reconnecting the temp sensor the glow plug circuit no longer worked and the car would not start. Disconnecting the sensor rectified the problem again, I know the 2 circuits are linked so we replaced the temp sensor with a new one, the car now starts fine however after only running for a few minutes the temp gauge heads steadily towards the hot side and eventually the temp warning light starts flashing, even though according to my mechanic the engine did not appear to be overheating. He has now suggested an electrical fault. Has any one else come across a similar problem or have an idea of what could be the problem, otherwise the next step is an auto electrician.

Thanks for any help.