Troubleshooting Trailer Wiring Where No Lights Work

Updated 09/30/2025 | Published 09/24/2025

Question:

Hi, I just bought the Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector C56327 for our 2024 Ford transit 150. I installed it, the tail lights were working, but when we plugged in the trailer, the trailer lights did not work. We got another harness thinking it was that, but still the same issue. I have it wired to the battery under the driver seat, could that be the reason the lights arent working? Or could it be something else? Thank you

asked by: Matthew F

Expert Reply:

Hey Matthew, are you sure the problem isn't the trailer taillights? Do you have a circuit tester that you could test the pins of the 4-way with to see if you can find out if the problem is for sure on the vehicle or trailer side?

expert reply by: Jameson C

Matthew F.

9/25/2025

Hi, It is not the trailer. The trailer works with my other trucks. I have bought other harness for our Mavericks and they work fine with this trailer. Not sure what it could be.

Jameson C.

9/29/2025

@MatthewF Is the battery under the seat for sure a 12 volt battery? It should be but I tried to look up that info and wasn't able to verify that.

Matthew F.

9/30/2025

@JamesonC Yes it has the 12v battery under the seat.

Jameson C.

9/30/2025

@MatthewF Do you have a circuit tester like the part # PTW2993 so that you could test for voltage on the input and output side of the converter box?