'76 temp sender wire

[maxreps]

Could anyone identify which wire should go to the coolant temp sender? This is due to a recent engine swap and have 2 possibilities for the correct sender wire. both are green. 1 comes from the passenger side along the firewall (no voltage when key on) and the other from the drivers side along the firewall (batt voltage when key on). Initially I hooked up the passenger side wire thinking it was that one. But no temp registered on the guage. So i figured it was the other one but checked voltage before connecting, and found battery voltage. I have not tried it because I dont wanna ruin anything.

[willett]

Which motor you have? Find the sensor and follow the wire.

[Jonboy]

That should be your wire. It will have a rectangular plug on the end, and that should have a notch out of one side.

[maxreps]

it's a 350, I'll give the one with battery voltage a try. I was leaning that way since it does come from the drivers side in the "loom"/harness but assumptions are bad.

[Robert8096]

Don't connect the 12v wire, you are going to short something out. The temp unit works off a resistance to ground theory. 12V is supplied to the gauge thru the gauge cluster. The green wire goes to the sender unit that grounds to the engine block. The sending unit varies the resistance to ground which moves the needle on the gauge.

Ground the green wire that has no voltage and with the ignition in the run position see if the gauge pegs out. If it doesn't then check the green wire for breaks and see if the gauge has 12 volts where it plugs into the cluster.

If you have 12 volts at the gauge and the wire checks out then you either have a bad sending unit or gauge. There are two types of sending units, one for idiot lights and one for a gauge. Make sure you have the correct one.

Good luck

[Dead Parrot]

I just finished swapping temp gauges. With the ignition on, you should have 12v open circuit on the sending unit end. Shorting the end to ground should give a full hot reading on the gauge, which is a quick test of gauge and wiring.

The problem is that other things also use green wires with 12v on them in that area. Choke heat and AC idle advance solenoid are a couple IIRC. Shorting those to ground can be somewhat energetic.

If you are into electronics, a 100 ohm resistor is about right to get a good deflection on the temp gauge in a 75. And if you have found some other green wire, not much will bad will happen. A small automotive light bulb can work as well.