When i had a FW the harness ran along the left frame rail next to the gray tank. Id look at the wire where the connections are and see if corrosion has migrated under the wire covering. Sometimes it can travel pretty far and it usually looks black Often times its green or white on the connection but the black stuff can travel up the wire. If you don’t see evidence of that make the repairs and seal all the connections. Dont use silicone I try to solder all the wires and coat with the correct grease and heat shrink. Some like the crimp and heat connectors. Tape the area over well to keep the moisture out.