Troubleshooting Trailer Wiring Harness That Stopped Working

Published 08/09/2021

Products Featured in This Question

T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(543)

$49.26

Hook Probe Circuit Tester

(62)

$13.33

Question:

I installed this harness last year and worked fine up till now 10 mos. with no issues. Had a broken wire on my boat trailer which I then fixed. Afterwards, after testing trailer lights to make sure all worked they did, I hooked up trailer to car and got no lights. Tested #118438 wiring harness with a LED 4 prong test plug but got no lights. Tested ground to battery 12 volts, tested pins with head lights and then hazards no voltage. 7.5 amp fuse tested good but I replaced it anyway. Your previous comments regarding similar situation suggests converter shorted out due to wiring fault on trailer but why didnt 7.5 amp fuse blow first? Whats the point of fuse if it doesnt protect the converter? And why would broken wire on trailer cause converter to fail? Can the converter be ordered seperately or do I need to buy the entire harness?

asked by: Ken

Expert Reply:

I wish the fuse would have blown instead of what seems to be the converter box but in your situation that's just how it seems to have gone. You can test this with a circuit tester like # PTW2993 for voltage on the input side of the box as well as on the output side of the box. If voltage is going in but not coming out of the box like it sounds like is going on then the issue is the box and you'd have to replace the entire kit since they are not available separately.

expert reply by: Jameson C