Temperature gauge help

[vettedad61]

On my 1972 c10 with factory gauges I recently restored the whole truck, new factory correct wiring harness, new cluster schematic and sending unit.

I hooked everything up and recently got the truck running after restoration, The temperature gauge is original and the needle doesn't move? I have used a test light and tested power at the sending unit and also at the connections on the back of the temperature gauge. I don't show it getting power at either spot

Can someone help or give me starting point to find the problem? Thank you!

the fuse panel is glass style fuses.

[ray_mcavoy]

Here is a diagram of the printed circuit on the back of the cluster:



As you can see, power for the temperature gauge comes through a trace that leads back to pin #3 on the cluster connector. That also powers your fuel gauge ... is that working okay?

If the fuel gauge is not working either, use your test light to check for power on the #3 terminal of the cluster connector. It should be a pink wire.

If you have power on the #3 terminal, but not at the fuel and/or temperature gauge, check for a bent/distorted #3 terminal in the cluster plug. Or for a damaged trace on the printed circuit.

[vettedad61]

Fuel gauge does work as well as the rest of the gauges, lights blinkers tach etc.

I will check #3 on the cluster, should I be able to get the test light to work with the key in the on position without the truck running? Also should I show power at the wire connection at the ending unit on the intake manifold?

I need electrical for dummies instructions lol

[72MARIO]

if you put the wire that goes to the temperature sender to ground does the gauge move to hot ?

[vettedad61]

Ray, great diagram, thank you!

Ok I just checked it out, the circuit panel on the back of the cluster was brand new, the wire is melted or damaged that goes from the connection #3 pink wire to the fuel gauge and the temperature gauge.

Any idea what caused this? Should a fuse blow before the the wire melts? I need to order anew one but want to make sure it doesn't do the same thing?

I only see one light brown wire that goes from the fuel sending unit on the tank to the fuse box labelled fuel. No fuse... The wire is new

72mario I tried your suggestion and then found the melted wire. Good info for me to try in the future. Thank you

[ray_mcavoy]

Originally Posted by vettedad61

Ray, great diagram, thank you!

You're welcome. I can't take credit for creating the diagram though. It's been posted on this site numerous times in other threads.

Originally Posted by vettedad61

Ok I just checked it out, the circuit panel on the back of the cluster was brand new, the wire is melted or damaged that goes from the connection #3 pink wire to the fuel gauge and the temperature gauge.

Any idea what caused this? Should a fuse blow before the the wire melts? I need to order anew one but want to make sure it doesn't do the same thing?

That sounds like you have a short circuit to ground. I don't have one of these clusters handy at the moment to refresh my memory, but I think there may be an insulator strip or insulator washers that keep the temperature gauge's hot terminal from making contact with the grounded metal case of the cluster. Check to make sure you're not missing any parts like that.

And before plugging it in again after making repairs, use an ohmmeter to measure the resistance between the printed circuit trace #3 and ground (cluster case). You should get a reading due to the internal resistance of the fuel & temp gauge coils. But as long as it's not really low or zero (dead short), it should be safe to plug in again.

The pink wire feeding terminal #3 should be protected by the 3 Amp "CLSTR FEED" fuse. Check to make sure a larger amperage fuse didn't accidentally get installed in that location. That could be a potential reason for the wire and/or printed circuit trace to melt before blowing the fuse.

Originally Posted by vettedad61

I only see one light brown wire that goes from the fuel sending unit on the tank to the fuse box labelled fuel. No fuse... The wire is new.

That's normal. The light brown wire leads to the fuel sending unit. It simply passes through the fuse box, using it as an intermediate connection point. Since the fuel gauge shares the same feed as the temp gauge so it too should be protected by the 3A cluster feed fuse.

[VetteVet]

Originally Posted by ray_mcavoy

You're welcome. I can't take credit for creating the diagram though. It's been posted on this site numerous times in other threads.



That sounds like you have a short circuit to ground. I don't have one of these clusters handy at the moment to refresh my memory, but I think there may be an insulator strip or insulator washers that keep the temperature gauge's hot terminal from making contact with the grounded metal case of the cluster. Check to make sure you're not missing any parts like that.

And before plugging it in again after making repairs, use an ohmmeter to measure the resistance between the printed circuit trace #3 and ground (cluster case). You should get a reading due to the internal resistance of the fuel & temp gauge coils. But as long as it's not really low or zero (dead short), it should be safe to plug in again.

The pink wire feeding terminal #3 should be protected by the 3 Amp "CLSTR FEED" fuse. Check to make sure a larger amperage fuse didn't accidentally get installed in that location. That could be a potential reason for the wire and/or printed circuit trace to melt before blowing the fuse.



That's normal. The light brown wire leads to the fuel sending unit. It simply passes through the fuse box, using it as an intermediate connection point. Since the fuel gauge shares the same feed as the temp gauge so it too should be protected by the 3A cluster feed fuse.

Excellent post Ray!!!

[Purple67C10]

I've had some thread sealer one time actually stop the sending unit from getting a good ground through the threads. Cleaned it off and it started working just fine. Might be something to look at.

[vettedad61]

Here is the link to my build thread
http://67-72chevytrucks.com/vboard/s...d.php?t=640419