Yet another temp gauge question

[DWX 9929]

‘71 c-10. Vortec 350. My temperature gauge was unhooked when I got it. Probably because of the different sending unit. Got the proper sender but haven’t started it yet. Gauge presently reads full hot even with the battery disconnected. Does this mean that the gauge is bad?
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[John H.]

The gauge works by having 12 volt power to it and the sending unit is the ground. The more it grounds (gets hotter) the more the gauge moves to hot.

Without the battery on, the gauge can't work. If it pegs when power is on your are shorting (green wire connection) somewhere between the green wire on sending unit and the gauge.

[DWX 9929]

Originally Posted by John H.

The gauge works by having 12 volt power to it and the sending unit is the ground. The more it grounds (gets hotter) the more the gauge moves to hot.

Without the battery on, the gauge can't work. If it pegs when power is on your are shorting (green wire connection) somewhere between the green wire on sending unit and the gauge.

Yes, I know that. Problem is gauge is pegged with no power. I’m assuming that there’s a spring in the gauge to bring it back to cold?
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[dmjlambert]

I have a 1969 CST/10. With power removed the temperature gauge stays in whatever position it was when the engine was turned off. So usually my gauge is sitting a little left of center, where it was when I shut the truck off. If I come back later when the engine has cooled off, and start the truck or turn the headlights on, the gauge will swing to cold. If the green wire that goes to the sender is shorted to ground, the gauge will peg to hot. If power is removed by turning off the key and headlights, and then the green wire short to ground is removed, the gauge remains pegged on hot. When I start the truck or turn the headlights on, the gauge will move to whatever the current temperature of the engine is.

[TBONE1964]

Try this,

Run a ground wire from the lower center stud on the temp gauge to a known good ground and see what happens.

Also, pull the green wire from the sending unit, turn the key on and see what happens. If the gauge goes back to cold, then the sender is bad. More time than not when the gauge pegs full, it is because the temp gauge itself is not grounded properly.

Keep us posted,
Tom

[DWX 9929]

Gauge is working normally. Guess it does stay at the last position when key is turned off. Thanks for the input!
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