Troubleshooting Wiring Issue at Trailer Connector

Published 10/19/2017

Question:

Just put a replacement wire harness and lights on a boat trailer. The kit comes prewired to the 4 pin blade connector to I know the trailer wires are good. I have a 7 pin plug in adapter to 4 pin flat blade for the receiver of the trailer. When I pug in the flat blade connector I get running lights but no brake lights. When I depress the brake I get no trailer lights. Turning on the right signal results in a 4 way condition on the trailer but right signal seems ok. I checked the voltage on the 4 pin flat blade of the 7 pin adapter and when the running lights are on I get 12.48 V from the the male pin to the first female pin to the right and 0.06 on pins 3 and 4. Turning on the left signal pin 3 of the 4 pin flat blade connector turns on and off from about 12.35 V and Pin 2 seem to from 12.48 to 12.40 and back to 12.48 in sequence with the turn signal. Same results on Pin 4 of the 4 pin flat blade connector when the right turn signal is turned on. When I remove the 7 pin to 4 pin adapter and try just the factory installed 7 pin connector I get the same results? Any help is appreciated. Thanking you in advance

asked by: Mr. V

Expert Reply:

It sounds like you have functional issues on the vehicle side of your connection. I recommend starting by cleaning your terminals of your connector really well and then using a circuit tester like # PTW2993 to check your functions as you test each one on your 7-way. Corrosion or debris can cause these types of issues to occur. I've attached an article to assist with the terminal locations and corresponding functions for you to test.

It sounds like you may have a bad ground wire on that trailer connection or on your trailer if this issue only occurs when connected. I recommend making sure it is bare metal to metal connection and you may even want to splice your ground wire to add a connection if using a jump wire to test it solves your issue.

Once you have tried this, if you still have issue let me know and we can continue to troubleshoot.

expert reply by: Jason S