[70StepsideC10]

I just bench tested a couple of gauges I have. One of them was installed in a cluster (not installed in a truck) and the other was just a spare gauge. The gauge installed in the cluster has a blue resistor, the spare one has a red resistor. For the blue resistor I measured 83 ohms when the resistor was removed from the gauge, and the same when it was installed on the gauge but the circuit board was not connected to the gauge. When I reconnected the circuit board to the left and right terminals, the resistor measured 61 ohms. The red resistor on the spare gauge measured 85 ohms when both removed from and installed on the gauge.

Below are resistance values (to ground) for the stock temp sender for these gauges. I found these values online and tested both my gauges and they were fairly close to these numbers. If you want to test your gauge rather than just pegging it hot or cold by grounding or opening the sender wire you can use these values. If you can get your hands on a potentiometer (variable resistor) you can connect that in place of the sender and vary the resistance to ground to test the gauge. I think you said in a previous post you confirmed the wire from the sender to the gauge was good. If this is the case, just disconnect the wire from the sender and connect it to one side of the potentiometer, and connect the centre terminal (adjustable wiper) of the potentiometer to a good ground. Vary the resistance of the potentiometer to the values below and see what your gauge shows, just use your ohm meter to check the resistance of the potentiometer as you adjust it. You will of course have to have the ignition on to power the gauge while doing this. If you can't get a potentiometer you could also just get resistors that are approximately these values and connect those between ground and the sender wire.

Left Line (Cold) - 350 ohms
Middle Line - 76 ohms
Right Line (Hot) - 51 ohms