Gary RV_Wizard
Site Team
The WFCO manual won't help identify what is on the #5 fuse - that was determined by the trailer builder. And maybe some subsequent owner mods. I've seen mods to illuminate the trailer marker lights while parked on shore power and similar seemingly innocuous wiring changes. Nor can we tell at this point whether there is a short or just an intermittent overload of the #5 circuit. It's even possible that the trailer power is backfeeding into the tow vehicle when connected. It shouldn't, but it can happen. Connecting the trailer plug to the vehicle completes a circuit between the trailer battery & tow vehicle to enable charging while underway. Power is supposed to flow into the battery from the tow vehicle, but the path is there to go either way unless a diode is present.
I think I would start isolating the trailer towing circuits from the trailer "house" circuits in hopes of finding where the interaction with the #5 fuse it. That won't help if the problem is an intermittent short in the house wiring that is triggered by movement, but you have to start somewhere. It's pure guesswork (or wire tracing) until you can narrow things down.
Another approach would be to split out the loads on the #5 fuse, temporarily putting each on its own fuse. Maybe wire a small fuse bus to the #5 fuse and connect the various feeds to separate fuses on the new sub-bus. But that assumes you can find those separate branches (pump, CO, etc).
I think I would start isolating the trailer towing circuits from the trailer "house" circuits in hopes of finding where the interaction with the #5 fuse it. That won't help if the problem is an intermittent short in the house wiring that is triggered by movement, but you have to start somewhere. It's pure guesswork (or wire tracing) until you can narrow things down.
Another approach would be to split out the loads on the #5 fuse, temporarily putting each on its own fuse. Maybe wire a small fuse bus to the #5 fuse and connect the various feeds to separate fuses on the new sub-bus. But that assumes you can find those separate branches (pump, CO, etc).
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