That big 850W fan needs some big wires and a way to safely deliver the current. I am going to use a 100A automotive breaker by Blue Sea. I’ve been using one for the rest of the Auxilary Power on the Jeep for years now and its been working great.

I cut a new battery hold down and mounted the breakers on top. One goes to the rest of the auxiliary system and the new one (its clean!) will route to the fan.

Next is to wire 8AWG wire from the breaker to the fan. I also have an off shelf PWM fan controller I will use till I get mine designed and built.