82 720 engine temp wiring

[Away8777]

Hello. I purchased a 82 720 with the z22 engine in it and I've been slowly going through wiring under the hood. The temperature gauge has never worked and I noticed it looks like the wiring has been disconnected I'm wondering what wire is the one that needs to be connected to the sending unit there are 3 that are yellow with a blue stripe I'm almost positive it's one of these from the research I have done just need clarification thank you.

[Away8777]

I have a picture on my phone but am not sure how to post it 

[datzenmike]

Look closer. The temperature sender wire is Yellow/Black stripe. It should be near, and reach the sender near the thermostat. Ground this wire and gauge should climb to full HOT. If not the problem is the gauge or the wire to it.

[Away8777]

Ok thank you I will try when I get home just to clarify the wire that goes to the sender will not have power or ground on it when not connected correct?

[datzenmike]

With the ignition on it's power to the fuse to the gauge to the sender to ground. The sender varies the resistance to ground with cold the highest resistance and no reading, to almost no resistance to ground for hot. You can't hurt anything if the wire is grounded, it just reads hot.

[Away8777]

Thank you datzenmike. I found 2 wires that are in the same wire harness both are yellow and black and both do exactly as you said they would with the test light on them both also make the gauge move when sent to ground with my power probe. One has a square connector and the other a round connector I would assume one is for the z22 and the other for the z24? I tried to connect the round connector to my sensor and let the truck idle for about 30 min but the gauge never moved? Thoughts ? 

[bottomwatcher]

Bad sensor. You can check with an ohm meter the resistance in the sensor 

[datzenmike]

If you ground the wire to the intake and the gauge works (reads HOT) but does not work when connected to the sender, then the sender is faulty. They are cheap and easy enough to change.

[Away8777]

Ok I figured as much. It's strange to me there is also a aftermarket engine temp gauge in the truck that was already in the truck when I got it that is installed just above the thermostat housing and it has never moved either. Yesterday when working on the truck I decided to test the gauge out by boiling some water and putting the sensor in the pot and it worked I re install it in the truck and let it run for a while and no movement from the gauge. I have seen some things on here about engine coolant not getting up to temp does this seem like it could be an issue in my case. Either way I am going to buy a new sender. Thank you.

[datzenmike]

Maybe not securely grounded to the intake? Does it have plumber's teflon tape on it or maybe anti seize paste that might insulate it?

[Away8777]

There wasn't any on the after market one and I haven't pulled the OEM one yet but I will hopefully get to it at some point today also when testing the wires and grounding them out the temp gauge never actually goes above half way is this normal?

[datzenmike]

It should read full HOT. Try a known good ground like the battery ground cable which is right beside the thermostat.

 

Does your fuel gauge read accurately?

[Away8777]

I will try that I used my power probe which should send ground directly from the battery ground. The gas gauge works how accurate it is I'm not sure of I have never actually filled the tank up completely with the way gas prices have been🙄.

[Away8777]

So I ground the engine temp wire directly to the battery ground cable and it still only goes up about a quarter of the way same result when I probe with with ground from my power probe.