Troubleshooting Trailer Lights Not Working on a Boat Trailer Towed by a 2008 Kia Sorento

Question:

bought wiring harness worked great pulled a boat a few times then one day it running light left side brake light right side checked connections and fuses all good bought etrailer wirring harness mounted it on vehicle because i thought mod unit bad why it was replaced ran vehicle 3 months never used until 4-22-11 hook up trailer and noticed no trailer lights checked connection and fuses all good what is going on thank you...........

asked by: Clay C

Expert Reply:

There could be several issues that are causing the trailer light problem you are experiencing and I can help you troubleshoot. First, we need to determine if the problem is on the vehicle side or the trailer side. You can start by testing the vehicle side 4-Way trailer connector.

using a circuit tester like # PTW2993, test the pins on the vehicle side 4-Way for the proper functions. If they are working properly then you know the problem is on the trailer side. If they are not working correctly, you can check the wires going into the converter box. If the signals coming in are correct, but wrong going out, then there is something wrong with the converter and the harness will need to be replaced. If the signals are wrong going into the converter, then something is wrong with the vehicle wiring or this is a missed or bad connection.

After you eliminate the vehicle as being the problem, you can move on to the trailer. Since this trailer has seen some marine use, corrosion could be the problem. Check the vehicle side and trailer side connectors for corrosion and clean them out to see if that solves the problem.

If you are still having trouble, make sure that the main ground wire from the back of the trailer connector is attached to a clean and corrosion free bare metal surface on the trailer frame. You will want to do the same with the tail lights. Trailer tail lights usually ground through the mounting studs and they, too, will need to attach to a clean and corrosion free bare metal surface.

You can also check the wiring on the trailer to make sure there are no nicks, cuts, or loose connections anywhere that me be causing the light failure.

expert reply by: Michael H