'76 Bronco Temp Sensor Pegged w/ & w/o being plugged in?

[Pruneda]

Have a '76 Bronco 302 in California.

Prepping for Smog. Warmed her up and noticed the Temp Gauge was pegged. Did some Googling and decided to test uplugging it then turning the key 'on.' With it the sensor plugged, and unplugged the need pegs to the right. I assume original cluster. Other temps/alternator works fine. Could this be due to a low battery or is this too old of tech to misread due to low/no voltage?

EDIT - Need goes full 'off' (left) when ign is off. Just pegs with or without the sensor connected (full right,) when acc/engine is turned on.

Easiest way to fix this? Id like to keep the cluster. Is it possible to rerun a wire from the sensor to inside the cab and just pull out the cluster a little and connect a new wire?

Other tests I can perform as a newbie of sorts?

 

[Broncobowsher]

Other temp gauge is fine? Is there more than one temp gauge?
Ampmeter is unrelated, does not use the IVR that the factory temp/oil/fuel gauges use.

Presuming you meant to say the fuel and oil both work fine, only the factory temp gauge pegs full hot even without the sensor hooked up.
You have a short to ground in the wire from the temp gauge to the sender, or the temp gauge is shorted internally to ground.
On the back of the gauge there are 2 wires. One daisy chained to all 3 gauges and the IVR, leave that one alone. Disconnect the other one.
Gauge still pegs full hot, bad gauge
Gauge stays full cold, wiring issue. Put it all back together and disconnect the 3-wire plug from the body to the engine. It has 2 wires for oil and temp sending units and a third wire for ignition coil power. This will tell you if the short in the harness is engine side or body side.

All that can be done without any tools at all.

 

[Pruneda]

Other temp gauge is fine? Is there more than one temp gauge?
Ampmeter is unrelated, does not use the IVR that the factory temp/oil/fuel gauges use.

Presuming you meant to say the fuel and oil both work fine, only the factory temp gauge pegs full hot even without the sensor hooked up.
You have a short to ground in the wire from the temp gauge to the sender, or the temp gauge is shorted internally to ground.
On the back of the gauge there are 2 wires. One daisy chained to all 3 gauges and the IVR, leave that one alone. Disconnect the other one.
Gauge still pegs full hot, bad gauge
Gauge stays full cold, wiring issue. Put it all back together and disconnect the 3-wire plug from the body to the engine. It has 2 wires for oil and temp sending units and a third wire for ignition coil power. This will tell you if the short in the harness is engine side or body side.

All that can be done without any tools at all.

Got into it a bit and created a few other problems. That said, I was able to emulate an issue by tugging on the Red/White Coolant Temp wire. When I did that at a certain point, it caused the Gauge to peg and not come down. Couldnt isolate exactly where the issue is but my plan now to rerun a wire and see if that solves it.

Found some other issues that im going to deal with during this escapade too. Including..finding a Red/Green wire under the dash near the center thats "looped" and very very warm to the touch if not "hot." Have no clue where its going as it comes from the center of the dash towards the cluster then loops right back. Tore back the taping and theres a good 1.5' of it that has an insulating rubber over it too. So...yeah.

Tugging on the harness going towards the dash caused the fuel gauge to peg..and oddly enough the fuel gauge to intermittently read 'high.' Not sure if related since it also had a funky orange jumper (likely for the aux tank that exists,) so i removed it and just rehooked it up. Gauge for fuel read fine until some tugging.

Plan is as follows: Run a new wire from Cluster to Firewall (as close as I can within reason since im a big guy in a small area,) and then replace the loom with the 3 senders on the engine since since thats only $19.99 apparently. See what comes of that.

EDIT - Do you happen to know the PN# for a universal connector to the Gauge Cluster 'studs' so I can replace the one thats OEM?

 

[Broncobowsher]

If all the gauges go high, that is probably an IVR issue. One of the most common issues is a bad ground. Not just the IVR to the cluster, but the cluster to the body ground as well. A weak ground and the dash lights taking the ground when the headlights are on can be confusing as well.

 

[rocknhorse76]

The looped red/green wire is the ballast resistor for the ignition coil. It’s supposed to get pretty warm, so no worries there.

 

[Pruneda]

If all the gauges go high, that is probably an IVR issue. One of the most common issues is a bad ground. Not just the IVR to the cluster, but the cluster to the body ground as well. A weak ground and the dash lights taking the ground when the headlights are on can be confusing as well.

Not all do. Yet temp gauge pegs if I pull on the loom wire individually. So something is up.