When probing, I was grounded to the battery, so wherever I saw 12v, 12v was there. it was really odd to see 12v on both sides of the relay coil until the fan switch clicked on, but in retrospect, since the fan switch is actually switching to ground, I suppose it's not that weird after all.
And yes, 100% the fan switch (or at least something in the fan switch circuit) is causing the fans to come on at the wrong temp.
And forgive my electrical terminology. I'm an engineer, just not an electrical engineer. I do, however, greatly appreciate how things are complicated when someone is using the wrong terms.
My question regarding where "low voltage gets pulled from" is expressed better with a longer question actually typed on a computer and not a phone. This is all about the relay and the ECU and how I understand the circuit to work.
The fans are easy. All they want are 12v and ground and they are good to go. They will get constant power on the appropriate-to-turn-in-the-right-direction polarity, and i'll ground them through the SPDT relay I have (pins 30/87). It's the relay coil and the ECU control that's the rub.
As you've said, the ECU is a ground switch. I understand this to mean that when switching a relay with the ECU, you have a low-voltage source on one side of the coil (86) and a ground source on the other side of the coil (85). When the ECU clicks the relay "on", it is essentially completing the circuit by allowing the coil to ground through the input pin (on the ECU). If this understanding is incorrect, then of course me wondering where that low-voltage source on pin 86 comes from is also incorrect.
How you describe it, I hook pin 86 directly to the battery. Pin 85 goes to the fan switch and the ECU? With this setup, won't the fans just turn on early when the fan switch grounds? How does the ECU provide control at this point? A bit more freaky is how the ECU doesn't get burned up by sitting on a 12v circuit off the battery. (this is why I'm thinking my understanding of how the ECU is "switching" is not correct). Frankly, I'm happy to take the fan switch out of the equation if that's an option, but maybe it's not.
I see the Redskins start in an hour, so thanks for taking time from a morning that may soon be dominated by football...