i installed an electrical temp gauge yesterday, I wanted more than just the factory gauge and have a question. there are three sensors by the thermostat housing. One is for the factory temp gauge, the other for the emissions/computer and the one not being used is facing the radiator and is the one i used.
As soon as i turn the key on the gauge jumps immediately to 120F. At running temp it reads 240F. I know this is not right, when i take off the radiator cap the water is hot but not 240. I decided to swap the connections between the factory gauge sensor and the one mentioned and  ???same thing happens. Faulty sensor? This is on a 1.6 in a Sammy. Doubled checked my wiring and grounds.. all looks ok

If the engine runs as suspposed to (high idol until warm, existing gauge at proper spot etc), I'd say it's your new gauge.

A couple of questions off the top of my head here.

Are you trying to install an after market gauge with a stock sensor?
Does your gauge require a sensor with a specific output?
Does the factory sensor output match the requirements of the gauge you are using?

Do you get where this is going?

I could be wrong, especially since I don't know what gauge you are using, but as far as I'm aware, tem gauges are calibrated to work with a specific sensor, so unless you're using the correct sensor or you know the sensor and gauge you have match one another, they will not work and you could in fact damage one or the other.

Fordem, thanks... The sensor provided in the gauge does not have the same thread so it won't work, and i thought i could get away with using the factory one. I made a few phone calls without getting anywhere.  I'm sure I'll have to use some type of bushing to get it to work.. to use the provided sensor. Any suggestions on where to put a sensor? Or does anyone have a particular gauge that will work with the factory one?