stock temperature gauge stuck on hot

[QuickStyle]

72 GMC 2500 402/700r4

my stock temperature gauge has been stuck on hot since i have had the truck. unhooking it from the sender it still stay on hot, checked for grounded wire with it unhooked from sender and its not grounded. removed gauge from cluster and manually pushed need back to cold, turned ignition on with sender wire disconnected and it stayed on cold, soon as i hook sender wire back up, it pegs to hot and stays there. I know it sounds like the sender is back, but why wont it drop back to cold when i unhook the wire. any ideas? thanks.

[gcburdic]

ttt

[Smitty]

I had a similar problem with mine. Some one told me to clean the contact area on the sending unit as well as the terminal on the wire. It seemed to work for mine.

[QuickStyle]

i think i might have found the issue, but don't know how to go about fixing it. the sender seems to be working fine, 900ohms cold 250ohms at operating temperature, now that might not be the correct sender, but it surely wouldn't cause the temperature gauge to peg hot. what i am getting is a 12v positive on the wire with the key on, i need to know if this is normal or not, and if it is not normal what could the issue be. My wiring diagrams show the dark green wire from the sender going to the ignition switch and then to the gauge, but doesn't specify what is happening to that wire in the ignition, I'm assuming its not suppose to get 12v positive.

[special-K]

A pegged temp gauge means it's grounded out somewhere.

[QuickStyle]

yes i understand that could be the cause of a pegged temperature gauge. however i have tested the circuit with a dvom and there is no ground on the wire while disconnected, key on or off, there is only 12v positive while key is on, i need to know if this is normal. if this is not normal then maybe that is why when i hook the wire to the sender with 200-900ohm resistance to ground its causing a short or something, causing the gauge to peg.

['79squared]

OK so if a pegged temp gauge means grounded some, my oil gauge does the same thing. Both stuck on high and when I hit the key they both jump a little higher until I kill the key then back to just plain hot. So,,,,, both grounded out ? Would you say?

[ole dollor]

never had one do this....might pull the cluster out and see if the circuit board might be broken or not plugged in correctly , or the wires have a problem...look at the circuit board and follow each line and see if its broken or blown into some where....you can use your ohm meeter and check it also....hope this helps.

[eric8]

What fixed the problem? Mine is doing this too. No ground in the wire.

[Lattimer]

Originally Posted by eric8

What fixed the problem? Mine is doing this too. No ground in the wire.

Try grounding out the back of the gauge. Sometimes it doesn't get a good enough ground through the cluster. Adding a ground wire fixed mine.

[Classic Heartbeat]

If I remember right your sending unit should read 620 ohms max witch would translate to about 70 degrees F. to about 96 ohms witch would be around 212 degrees F. Sounds like either you may have the wrong sender or the sender is bad. WES