Thanks for the info, Fave.
I do have the schematic from the factory manual. We did the relay jumper for initial diagnosis - it spun the high speed fan but not the low, that's why we went after the resistor. Replaced that and then when we jumpered again, the low-speed did spin, but not when the engine warmed up, so I changed the relay but that didn't help.
Just took the readings again, based on your post, got 12V+ on pin 3 and 0.0 ohms from pin 5 to ground. So OK there.
While I was out there I tried to get a reading on the engine coolant temperature sensor, and it seemed to be open circuit, which would be bad, although it's hard to get the probes in past the resonator. I'll test it again when I have more time to move stuff out of the way, but:
if the coolant temp sensor were shot, wouldn't the high-speed fan go silent also? Or is there a backup circuit that triggers the hi-speed, maybe from the temperature gauge sender? My temp gauge is working fine, and the hispeed fan always comes on when the engine gets real hot, and it never overheats. Knock knock.
