No power at temp gauge

[76burb]

76 3/4 ton suburban. All gauges work except the temp gauge. Replaced the sending unit, gauge still won't move. When I ground the sensor wire the gauge pegs past full.

I pulled the gauge and used a multimeter to test the receptacles where the gauge plugs into the cluster. Driver side plug should be 12v key power and top should be ground. I get -.02 on my multimeter when I test those. When I test passenger post(sending unit) and ground I get 11.6v.

What do I need to do to get power to the gauge. The key was on when testing.

 

[dd1990]

Sounds like wire going to senidng unit is cut or gauge cluster printed circuit is messed up. I would look up the temp wire on the 18 pin and see if you get any continuity

 

[76burb]

Sending unit wire seems to be good. What is the 18pin?
When I ground the sending unit wire to battery gauge pegs full. If I manually move the needle to the right and then turn the key on the needle goes back to cold.

 

[Ricko1966]

If you ground it and it pegs,then your getting power,you are not getting a controlled ground. Check continuity on wires from sender to gauge and sender to head.

 

[Rusty Nail]

I vote you've got a short to ground.

 

[Ricko1966]

Check continuity from the sender terminal to head on the sender with wire disconnected. Check hot and cold see what readings if any you get.

 

[Rusty Nail]

*and snap some pix

SNAP EM REAL GOOD!

 

[75gmck25]

Did you use Teflon tape on the sending unit threads? That can prevent getting a good ground to the head. Check resistance between the sending unit body and the engine and it should be zero.

 

[76burb]

Update-- I did find a small cut in the green wire. I replaced that section of wire and still have the same issue. Temp gauge stuck on cold. If I remove the gauge and move the needle to hot then replug the gauge back in it flips back to cold immediately. I have tried another gauge and that one does the same thing.

I also put my testers on both ends of my old sending unit while it was out of the block and got infinite resistance or the 1 on the far left of screen.

when I put the tester on the installed sending unit and then the other to the engine I got the same 1 on the far left side of the multimeter which I think means infinite resistance

 

[gmbellew]

infinite resistance means it is open and has no continuity, right? sounds like a bad sending unit?

 

[Ricko1966]

Update-- I did find a small cut in the green wire. I replaced that section of wire and still have the same issue. Temp gauge stuck on cold. If I remove the gauge and move the needle to hot then replug the gauge back in it flips back to cold immediately. I have tried another gauge and that one does the same thing.

I also put my testers on both ends of my old sending unit while it was out of the block and got infinite resistance or the 1 on the far left of screen.

when I put the tester on the installed sending unit and then the other to the engine I got the same 1 on the far left side of the multimeter which I think means infinite resistance

Did you check either of them hot? Did you check continuity sender to head?

 

[76burb]

cold and out of the truck the sending unit tests about 600 ohms. I installed the sending unit and let the engine run for a bit to get hot and then tested the sending unit and grounded to a bolt on the ac bracket and got like 200ohms

Gauge still reads just above cold. tried a different used gauge and it reads the same. teflon tape removed from the new sender

I have also tested the resistors on the back of both gauges and they read roughly 85 and 95 ohms

 

[Ricko1966]

cold and out of the truck the sending unit tests about 600 ohms. I installed the sending unit and let the engine run for a bit to get hot and then tested the sending unit and grounded to a bolt on the ac bracket and got like 200ohms

Gauge still reads just above cold. tried a different used gauge and it reads the same. teflon tape removed from the new sender

I have also tested the resistors on the back of both gauges and they read roughly 85 and 95 ohms

Double check me but I think 74-78 cold reading should be 350 ohms. I'm thinking you have the wrong sender to the best of my knowledge there are 3 and all 3 are different resistance.

 

[76burb]

Ive got the sender with the round terminal that fits the Packard connector on the sender wire. I thought the later senders had a spade connector.

 

[Ricko1966]

Resistance