Luddite, I think you have it right. My bypass switch activates the relay and will not work if the relay fails. For this reason I carry a spare relay. It is a plug in relay and is easy to change on the side of the road. My original relay was a 30 amp rated relay and I replaced it with a 40 amp. So far with the bypass and heavier relay I haven't had any problems.
You could wire your bypass switch in at the fan wires at the relay and bypass the relay. Make sure you use heavy enough wire and switch.
Last edited by davewhite; 21/08/20 03:30 PM.