Troubleshooting Potential Corrosion Problem in 5th Wheel Trailer 7-Way Plug

Question:

I just brought the trailer home for spring cleaning notice the one wire blue was chewed in two. replaced bad section. Getting ready to haul the trailer back to storage I notice the running light were barely working, only some of them and the green wire was hot to touch in the junction box on the fifth wheel hitch. Disconnected the trailer from the truck. The number 4 pin on the trailer connection wire to the truck is carrying 14 volts. Is there supposed to be voltage from the trailer - cable to the truck when it is not hooked up? It seems to me a relay is acting up in the trailer.

asked by: Don

Expert Reply:

It sounds like you could have a corrosion issue inside your 5th wheel trailer's 7-way plug. What can happen is that after enough exposure to the elements corrosion can develop inside the plug where it is almost impossible to see but where it can cause two nearby circuits to become bridged together. This is a common issue and it is easily fixed by installing a new 7-way plug like # H20046 which you will connect at your junction box. Or you could use plug/junction box # HS381-9000.

If this is the issue it would explain why your trailer-mounted battery could be sending voltage back through the wiring to the truck and/or cause the green wire to heat up from that power leakage.

expert reply by: Adam R