I've been using a Painless Wiring #30110 thermostat switch for years it screws in my intake and I wired it as the ground for my fan relays it comes on at 195 off at 185 and I also wired in an override switch to the Painless switch.
They also have a Part# 30111 that is on at 185 and off at 170 both switches cost just under $40 each.
They also have a Part# 30111 that is on at 185 and off at 170 both switches cost just under $40 each.