I believe the red wire in the loom that you are seeing goes to the fuse panel INSIDE the coach. If this is the wire that you are describing, then the end that you are looking at goes to a large terminal on the blower motor relay. From that same blower motor relay terminal there another 6" wire that goes to the isolator. That wire to the isolator is a 16 ga. fusible link.

I hope I am describing the wire you are asking about.