Trouble shooting coolant gage - 66 Sat

[AR67GTX]

Trying to determine why the temp gage in my 66 seems to not be working. All new harness which I carefully went through and verified all wire indexing and continuity during replacement. Also I have an auxiliary mechanical temp gage under dash and it reads a pretty steady 180F when running.

I disconnected the harness terminal at the sender, hooked a wire lead to it, turned on the ignition, and momentarily grounded it. The gage responded immediately and went about half scale before I removed the wire from the ground. So I assume the gage is OK. Fuel gage works fine and I installed a new gage panel voltage regulator.

Then I hooked a multimeter to the harness terminal and grounded the other lead with the ignition on. The volt meter started cycling between about 6 or 7 volts and 0 volts similar to some time ago when I tested a dash instrument voltage regulator. Is the power to the sender unit fed from the low voltage side of the instrument panel regulator or should it have a steady 12 - 13 volts?

Checking the cold sending unit resistance between the terminal and ground/threaded housing shell, what kind of resistance should I be seeing with the engine temp around mid-60?

Anything else I could be missing or need to check? Hoping for a bad sender versus something more involved.

 

[dadsbee]

Good sender should ready somewhere between 300 and 340 ohms in a 70* shop. My pouched one was around 1400 ohms.
https://www.forbbodiesonly.com/mopa...er-bird-cleanup.173290/page-13#post-911682521

 

[RemCharger]

Regulated power to the gauge, gauge to bulkhead, bulkhead to sender, sender to ground.
Maybe try wiggling the violet sender wire at your firewall plug.

 

[AR67GTX]

Regulated power to the gauge, gauge to bulkhead, bulkhead to sender, sender to ground.
Maybe try wiggling the violet sender wire at your firewall plug.

 

[AR67GTX]

I did including pushing in on the end of the terminal with a small screwdriver to make sure it was seated all the way. Since I have power at the end of the plug from the gage VR I guess I have a complete circuit.

Going out now to check the sender ohms.

 

[RemCharger]

Good sender should ready somewhere between 300 and 340 ohms in a 70* shop. My pouched one was around 1400 ohms.
https://www.forbbodiesonly.com/mopa...er-bird-cleanup.173290/page-13#post-911682521

Thanks and agreed, 342 I just got from one here.
Found a junk one and threw it out

 

[AR67GTX]

Well, I beat you dadsbee, mine read 7,880 ohms both to the battery (-) and to the outside of the sender case. Guess I’ll see if Halifaxhops has any good ones in his stores.

 

[Jerry Hall]

Thanks guys, my original 67 GTX has a temperature gauge problem. One day it works perfect and another it doesn't register. I to have made all the above references. As I have never seen a temperature sending unit go bad, that was the last thing I was thinking. I guess it's time to replace that intermittent sending unit.

 

[AR67GTX]

I’ve had my 67 GTX’s gauge act up occasionally too. Doesn’t respond one day and then back the next. Fortunately it only acts up very rarely and not in the last year that I remember so I’ve not tried to get to the bottom of it.

 

[gtx6970]

Put a Test light at sender conne tor ...it should blink. Same for fuel sender..

Ground said connector and gauge should go to full.

Sounds like a bad sending unit