Troubleshooting Trailer Wiring Harness that Stopped Working Totally After Blown Fuse

Question:

Camper trailer A-Liner lights acting strange. 118304 T-one Wiring Harness purchased in May 2015 for 2006 Toyota Sienna Van with 4 to 7 pin adapter. The camper has a 7 pin harness. I liked the plug and playinch aspect of this harness. I purchased this adapter to replace one that I had badly damaged. At the time I checked the basic functions brakes and turn signals and running lights and everything looked good. Last week I blew the brake light fuse in the van while towing the trailer. I dont want to blow the brake light fuse, not have brake lights and have to bypass the shift lock. So I checked the function of the lights again. Running lights OK Hazard flashers OK Left and Right Turn Signals OK Brakes OK Brakes + Right Turn OK Brakes + Left Turn - Both Left and Right pulse slightly brighter Brakes + Hazard - Right blinks Left pulses slightly. This is odd. I checked the wiring to each tail light and everything looks wired correctly. I also bypassed the 7 wire harness and wired a spare 4 wire harness directly to the tail lights and they still were acting the same easy to do once one has access to everything - 5 wire nuts. Thoughts

asked by: Charles K

Expert Reply:

It sounds like you may have damaged the converter box of the part # 118304 when you blew the fuse and now it's not functioning properly.

What you can do is test for voltage going into the converter box and then test for voltage on the output side to see if the voltage is in the correct places. If voltage going in looks good but not coming out then the box is bad.

Before you replace it you will want to inspect the wiring of your trailer to see if you can find anything that would cause the box to short out like corrosion or cut/exposed wiring. These boxes don't usually go out unless there is a short on the trailer that takes it out.

If there isn't input voltage for the converter then the problem is the wiring of the wiring kit. You will need to check to make sure it's making a solid connection to the correct circuits.

expert reply by: Jameson C