Cooling fan wiring

I bought the vehicle from my father in law and I was told that the vehicle would over heat occasionally. I assume he is the one who did it but the cooling fan was wired direct to a toggle switch. It worked for a week or so when the fan stopped getting power. My thought as to why is that he wired the switch to the high speed side without a relay and it either burnt up the fan itself or the switch. Now the toggle switch and wiring was removed before a I received the Buick. My question is well two actually are. 1) What wire is the 12 volts constant so I can run a secondary wire from battery to see if both low speed and high speed fans are still operable? Number two is, I purchased an adjustable cooling fan controller but the only one a available was the Torqflo 733653 kit which did not come with a relay like the others. Do I just wire the aftermarket fan controller to the low speed fan and run another toggle to high side to manually turn fan on in case the low speed does cool the motor before I blow a head gasket? Any input would be helpful and thank you for you time.