Troubleshooting Right Side Trailer Lights That Are Dim

Updated 05/06/2015 | Published 05/05/2015

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Digital Multimeter with 42" Long Test Leads - LED Display

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Question:

I noticed that my right turn signal and rt tail light is dim on the trailer. I wanted to troubleshoot a bit further and hooked up a 4 way trailer light tester and the same dim light on the rt side. I unplugged the harness and re plugged everything and it is still dim. Any idea as to what it may be? I bought the harness from you maybe a year ago. Is it a faulty harness, dirty connections, ground? My lights are LEDs so they should both be super bright.

asked by: Adam

Expert Reply:

Since you trailer's right side turn and tail lights are dim, but still operate somewhat, the most likely cause is a bad ground at the light unit itself. If the main trailer ground were at fault this would affect both sides of the trailer so odds are that the issue is at the light assembly.

If the light uses a mounting stud for its ground remove the fixture and sand/clean the area to remove any paint, primer or grease that may be interfering with the ground connection. If the light uses a wire lead for its ground, such as # 271595, then clean the point where the ring terminal is attached.

If you have a voltmeter like # PT89ZR you can test the output of the vehicle 4-pole harness (with the trailer disconnected) to see if the voltage is the same on both left and right sides of the 4-pole. Please refer to the linked photo and article for more on testing.

expert reply by: Adam R