the fans i used were 12 volt, they were the type used in computers, i worked in a factory that made those type fans at that time so it was no problem to get them! my mule i made an adapter that moved the thermostat out and had a port coming off it so i could plumb it in before the thermostat like a car heater is. only trouble is that the mule doesnt realy have enough flow, it makes good heat but i think since the radiator hoses are only the size of heater hose there may be a better way to hook it up, maybe in series, i dont know how the factory mule heaters are hooked up. it tends to be a tricky balance between flow to the heater and enough flow to keep it circulating thru the engine, basicly it flows back thru the heater easier than up into the engine i think