MG Car Repair: 1977 MGB temperature gauge, gauge needle, temperature gauge

Question
I have a recently purchased 1977 MGB. The Temperature gauge does not work. The alternator was mounted upside down and broke the sending unit. I replaced the sending unit. Still does not work. When I ground the wire from sending unit it goes all the way to hot. I thought maybe bad ground to engine. I added ground to engine. Still does not work. I could check voltage if I knew what I was looking for. Thanks

Answer
Hi Herman,
The temp gauge is powered by a voltage stabilizer to drop the 12v down to about 10v but the method we used was to turn the key on and look at the gauge while someone unplugs the wire from the sending unit. The gauge needle will deflect one way and then have them ground the wire and the needle should deflect all the way in the opposite direction. That is a rough test of the gauge and wiring, but was almost always a method to separate the problem. If it did deflect each way then it was a sending unit failure and if it didn't deflect it was either the wiring, voltage stabilizer or the gauge itself.
I believe your car had the stabilizer on the firewall behind the instruments. If the fuel gauge is reading correctly than it is not the stabilizer as that gauge is also powered by the same stabilizer. The sending unit is just a temperature sensitive resister that changes the amount of connection to ground.
Howard