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For all my trailers (RV, utility, boat), I rip out (remove) the factory linear wiring design and replace with STAR design. Solder All connectors, cover the mar connector, and cover with liquid rubber. ALL brake wire runs("control wire" and its ground wire) are separate 10 Gauge thickness and all wiring inside plastic PVC/PEX piping and/or plastic wire loom. Thus, triple protection from road junk / road salt. Before and After upgrade with STAR design is like night and day comparison. And best of all, the electrical flow is now balanced.
For a few pictures, surf:
- click here for factory design - - click here for STAR design - - click here for wire support at wheel hub - - click here for PEX tubing - - click here for PVC junction box - If wondering, all my trailers get STAR wire design using thicker 10 gauge wiring to each wheel hub. Without hesitation. And, all my customer bought trailers get STAR wiring design as well.
For such an old trailer and knowing Brakes is #1 safety, I would replace with new Brake Assembles and brake hubs on each wheel hub. Thus, "NEW" parts - instead of trying to sand / wash old rusty parts.
If wondering, trailer tires should NEVER lock up on normal driving conditions. If they did, fish tail skidding (especially on wet / ice roads) is at extreme risk. The trailer should "dramatically" slow the attached Tow Vehicle but RV/TT tires should never lock up.
If using a Time technology Brake Controller, immediately rip out, trash it, and replace with motion sensor / inertia technology brake controller. Prodigy P2 or P3 are best electric Brake Controller to use.
Hope this helps.