Troubleshooting Trailer Wiring When Turn Signals Cause Marker Light to Blink and Both Tail Lights

Question:

I have a 5 wire 4 pin flat plug White, Yellow, Brown,Brown, Green . Some of the wires got ripped loose from the plug. I purchased Item # A35W42B and cut about a foot off of the plug end. I wired it color to color used insulated crimp connectors and used shrink tubing on ea. individual wire. Now when I put either my left or right turn signal on, both tail lights and side markers blink. What is wrong?

asked by: Stan F

Expert Reply:

It sounds like your connection may have some corrosion or your splicing has allowed the jumping of power from one function to another. I recommend first checking your vehicle side connector using a circuit tester like # PTW2993 to determine if the functions are shorting on the vehicle side causing that issue. I've attached a video to assist.

If the vehicle side wiring checks out, then it sounds like the color for color connection was not correct with the functions. The two brown wires (one run to each side) should be running lights and should not change with the turn signals. The green is the brake/turn on the right side and the yellow is the brake/turn on the left. I've attached an article with a diagram to assist. It sounds like your turn signals on each side are on the brown wires and because those are connected together you are getting the function on both sides and it includes the clearance lights wired to those sides.

It may be easier to get a new harness and keep the plug end then wire based on function to your trailer.

expert reply by: Jason S