4. We decided to mount the supplied heater switch to the dash in a hole that had been drilled for some other accessory at some point in the past. The switch is roughly in the middle of the dash, so driver and passenger can easily reach it and adjust the speed. There are four settings, Off, Low, Medium, and High. Wiring is pretty simple. We followed the included instructions and spliced in a 7.5-amp fuse to the supplied wiring.