Electrical wizzard? temperature gauge not working
 

Hi,
I own an imported Californian 911sc 1978 and my temperature gauge is not working.
I was looking at the electrical diagrams and I see that there should be 3 wires: a "+" a "ground" and the "black/green wire" coming from the sender.
They are all there and the "+" and "ground" are reading out fine.
I checked the black/green wire that comes from the sender and that is ok to.
How can i find out if

• the temperature gauge itself is broken
• or the sender is broken?

Thanks for your advise
Bruno - Bredene - Belgium

The sender is a resistor that changes resistance to ground as it heats up. If you touch the black/green wire to ground with the car running the needle of the gauge should rise to the top of it's range. That will tell you the gauge is working. Just put a jumper from the wire terminal of the sender to ground. Do it quickly for a short time as there should always be some resistance in the circuit. You don't want to overload the coil in the gauge. To test the sender use an ohmmeter to check the resistance from the shell of the sender to the terminal connection. Take a measurement when cold and then another one when the car is warm. It should change.

sound logic,
will try next weekend
Thanks !!

It works again !!! :) Thanks timmy2
the reason was that the previous owner mistook the "G" and "ground" on the gauge. He switched them....

• The "+" is very well marked
• The "-" has the ground symbol (the one with some smaller becoming parallel lines and one diagonal line on top of it)
• The "G" is for the green/black wire coming from the engine sensor.

Ah! the good feeling of getting it working again - thanks to timmy and all the Pelicans who've helped many of us.