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Discussion Starter #1
1969 original z-28--although the motor is now a gm crate small block.--while driving, the temp. gauge quit working. after investigating, i found the voltage regulater had stuck , melting the alternator wire. after replacing alternater. regulater and cleaning up battery acid and repainting a couple of places, the temp. gauge still doesn't work. i replaced the sending unit , but it didn't help.when i turn the ignition key to the on position, the temp. gauge needle pegs out to cold . any suggestions?
 

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Sounds like a ground issue at the sender or the gauge.
Are we talking OEM, reproduction OER, restoration correct Classic HQ, or aftermarket gauge pack?

Also when you replaced the sender did you use Teflon tape or pipe dope? If yes remove it since that may prevent or interfere with the ground to the block
 

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Ground the wire on the sending unit and gauge should read full scale hot.
 

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they are original console gauges--i used antiseize compound as it is an aluminum intake-i removed the compound, just to be sure--no difference--i removed the green wire from the sending unit, grounded it and turned the ignition on. the gauge went from cold position to pegged out to cold position. i was thinking it should have pegged out to hot.
 

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Reverse the wires on the gauge and test again. Should peg HOT
 

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i haven't messed with the wiring--it has been working like it was--but,since our last blog, i unhooked the plug behind the gauge and ran a jumper on the green wire to the other end of the same wire and found continuity , so assuming the green wire was making connection all the way through. then i plugged it back and tested the wire by grounding it out at the sending unit and it pegged the gauge to hot like it should. gauge still doesn't work, though.it still pegs out cold when i turn on the ignition is there a way to test the gauge itself? i warmed the engine up to see if was working--stayspegged on cold
 

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Engine cold, disconnect the sending wire and measure the sending unit stud to engine block, should read a high resistance, above 5000 ohms, typically. Hook wire to s/unit, gauge should read cold, or even pegged cold. Final check is to measure the hex (body of the s/unit) to ground and should be less than 1 ohm resistance. If not, s/unit is not grounded through the threads to engine block/head.

Warm engine up to operating temp, top rad hose will be hot. Unhook s/unit wire and measure s/unit stud to ground. Should read around 200 ohms when coolant is hot and gauge should show a hotter temp indication, typically, a 180°F thermostat, needle typically should be at 10 o'clock mark.

The above statements are good if there is battery voltage to the correct terminal of the gauge. You can check the gauge using the ohmmeter function across the gauge itself no connections of the gauge to anything else. You may have to reverse the leads to get it to work, peg cold one way and peg hot the other polarity.
 
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