# temp sending unit troubles



## 6t8goat (Apr 2, 2015)

my temp sending unit is pinned past the hot marker to where it is not visible. I removed the wire from the sensor and grounded it. with key on, needle goes to hot position. installed a new sensor, connected wire, need pinned past hot again. unit was working fine before I pulled engine to have it rebuilt. now that its back in?? well ,you know.....it never ends. any help is appreciated. thanks, tom :banghead:


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## Rukee (Feb 8, 2007)

When you disconnect the wire with the key on does it go to cold?


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## 6t8goat (Apr 2, 2015)

no. it is pinned past the hot. you can't see the needle. when I ground the wire it comes into view and stops at the "H".


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## BearGFR (Aug 25, 2008)

Almost sounds like you've got a temperature switch in there (for a light) instead of a sending unit for a gauge...

Bear


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## JohnGoat (Aug 21, 2015)

I think the idiot light switch/sensor has two terminals, where the gauge sensor has one?


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## BearGFR (Aug 25, 2008)

No sir, they both just have one connection. They only need one. The switch sensor is a simple off/on switch. When the coolant temp gets high enough, the switch closes a path to ground which turns on the light.
The temp sending unit is a resistor that varies in resistance value in proportion to engine temperature. It also connects to ground. What your temp gauge is actually reading is this resistance.

Bear


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## JohnGoat (Aug 21, 2015)

I have a '70 with a 455. When I bought it, I was told it had the wrong temp sensor (it has idiot lights), it has the single terminal. I first tried to get an idiot light temp switch at Autozone, but all they showed was a gauge sending unit. I had them check earlier years and I think 68 or '69 listed an idiot light temp switch and it had 2 terminals. Since then, I believe I have figured out that the block is from a '74 or '75 Trans Am, with '67 428 heads on it. Not 100% certain. Anyhow, I left the gauge sending unit in it as I bought rally gauges, so I didn't check on the temp sensor situation with the '74/'75 455.


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