In the summer time here in Santa Clarita it can get up to 110F on a regular basis. My cooling system hovers around 87-92C normal driving and can get up to 100C in traffic with the A/C on. Those temps don't bother me too much, I'm just curious about the wiring of all the sensors. I want to know what drives the aux fan. If it indeed has just the a/c recv/drier pressure switch or if it also has the 100C switch for engine coolant temp. It's a 1984 300SD. I've gone through the archives and can't find any specifics about that model. I've read other newer models have 2 stage or 3 stage operating modes for the aux. fan. I did come across a post that suggests that the early 80s models don't have a coolant temp switch. I just want to confirm this. After all, if the aux fan should come on with high coolant temp also, I want to fix that. Thanks for all the input!