Same as checking the Gas gauge, ground the sender wire & see if the gauge moves.
Be careful though, if grounded too long it'll smoke the gauge for sure. I use a wire with clip leads to ground, get in the car & turn the key on & if it moves & gets close to the high side of the gauge ( HOT ) turn the key off. Gauge is good. If it doesn't move the wiring or gauge is bad & you have to troubleshoot further.
If the fuel gauge or Oil pressure also don't work right it might be the instrument voltage regulator. If it just the temp them the Regulator is OK.
Butch
