MG Car Repair: MG temp gauge, voltage stabilizer, gas gauge

Question
Howard, A friend bought a MG and asked me about the temp
gauge-- it goes straight to hot when ignition is turned on from cold start and stays at hot. It has a new sensor installed in the engine and when that wire is removed the gauge goes to cold. The gas gauge seems to be OK and drops with fuel use. I understand these two gauges share a stabilzer behind the dash. Any ideas? Test procedure? This is a 1972 model.

Answer
Hi Marcus,
Yes, they share the same voltage stabilizer as a power source (about 10v). If you checked to see that is where the power comes from and it has a good ground and the sensor has been replaced, the only thing left in the system is the gauge it self and the wires.

At the dealership I considered making up a test stand to test gauges but that would have cost as much as a gauge. The only tests we done is what you did. Key on, read the gauge and remove the wire from the sending unit and watch the needle deflect and then short the wire to ground and the needle would deflect the other way. If your needle is fully deflected all the way in either direction when you just turn the key on, you either have a short in the wire or a bad gauge.
Howard