Troubleshooting Malfunctioning Trailer Right Turn Light

Updated 04/01/2016 | Published 03/30/2016

Products Featured in This Question

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

(466)

$31.76

Curt Powered Tail Light Converter with 4-Pole Flat Trailer Connector

(1783)

$84.64

Hook Probe Circuit Tester

(65)

$13.35

Question:

I have a 2003 GMC Yukon Whenever I turn my left turn signal on both turn signals flash but when I turn my right signal just the right one flashes like normal. I have a tester and whenever I plug it in without the vehicle on the right turn signal light on the tester lights up.

asked by: Benjamin R

Expert Reply:

I am not sure if you are referring to your truck's own lights or the lights on a connected trailer but since you referenced 4-pole wiring harness products such as # 118384 I'll assume you're talking about the lights on the trailer misbehaving.

When a 4-pole harness exhibits weird behavior like what you're seeing often the cause is a simple one: a weak ground connection. Check your main trailer harnesses grounds, both the ground wire on the vehicle harness and the one on the trailer. You may just need to clean off the metal surface at the grounding points, or possibly relocate them to a new clean bare metal spot. Clean metal-to-metal contact is critical.

If you confirm a good ground on the vehicle harness and repeat the test with the trailer not connected (using a tester like # PTW2993) and you still find the right turn signal is on all the time, then the harness is likely damaged and needs to be replaced.

If you need a new aftermarket 4-pole harness, you can use part # C59236.

expert reply by: Adam R