Toyota Repair: Fan on all the time when key on, corolla dx, fanis

Question
1990 Corolla DX: The fan is on at all time even when engine is cold; I try disconnecting all three sensor near the thermostat but the fanis still on; ONLY when I pull off the 30A main fuse will it stop.  Any thoughts?

Answer
The cooling fan works when the temp sensor is open, this is a bi-metal sensor that opens when the temperature goes up so disconnecting it doesn't help, I suspect the the cooling fan temp sensor on the bottom of the radiator is the problem, try replacing it.