Saturn Forum - Saturn Enthusiasts Forums - Temp gauge not working... diff between ECTS & CTS?

I have a '94 SW1 that I just finished rebuilding the engine on. It runs great now, and I'm just trying to iron out the few remaining bugs... First thing is that the temp gauge doesn't work. I ran it enough to make sure the engine got up to temp, checking to make sure coolant was flowing by touching the upper radiator hose. Everything seemed to be fine, but the gauge wasn't moving at all. I had earlier replaced the ECTS with a new brass one (before the rebuild) and the gauge was working fine. I have the SOHC engine with both the temp sensor and the temp sender. If I have it right, the ECTS is the one closest to the upper radiator hose (2 wires, black & yellow), and the temp sender is about an inch lower and a few inches back on the head (1 dark green wire), right? I thought maybe I hooked them up backwards since they have the same type of plug, so I switched them, but it made no difference. So I switched them back. I was playing with them while the engine was running, and weirdly, when I pushed in a little harder on the ECTS connector, the engine started loping/idling rough... when I let it go, it ran smooth. I guess one question is what is the difference between the 2 sensors, if any, and to make sure which is which... Should I also replace the temp sender?

Also one other thing, I started it up and let it idle for a while to get it up to temp, and after a couple of minutes, the fan came on. I checked the engine and it still felt pretty cool, and nothing had started flowing through the radiator hose yet so it obviously hadn't gotten up to temp yet. So why did the fan come on??