Troubleshooting Yellow Turn/Stop Circuit Not Working on 5-Way Install

Published 09/18/2023

Question:

Have a F-150 with factory round trailer plug. When we plugged in a 5-way flat connector using an adapter, everything worked, except the left turn signal. It did not work. The output on the adaptor attached to the tow vehicle tested as good as did the trailer when hooked up to a test box. We also tested the round plug, and it was good as well. Finally, when we used a 4-way flat adapter and plugged the 5-way into that, everything worked on the trailer running lights, signals, etc. excepting, what that 5th plug operated. Any thoughts on what is up?

asked by: Daniel S

Expert Reply:

It's either going to be corrosion on the pin of the 5-way that needs to be cleaned off with sandpaper or it's a problem with the wiring. If this is a new install I would assume it's the connection of the left turn circuit (yellow wire) to the vehicle wiring.

expert reply by: Jameson C