Ok, with the black top of the switch facing up, pins 1 and 8 are at the top.
Pin 1 is a 10ga red wire that is a direct battery feed. It should have 12v at all times. It is a wire from the battery feed circuits.
Pin 8 is a 10ga dark blue wire and supplies 12v to the fan blower motor. It is a wire from the climate control circuits.
So it seems likely you are pulling too many amps through that circuit for the blower motor. This could be many reasons such as a motor going bad, poor ground or loose connection. It could also be none of the above but rather too small wire for the circuit. IDK what the engineering specs called for on that circuit.
But that should cover your Qs. Feel free to ask more if needed