Troubleshooting No Running Lights When Hooked Up to U-Haul Trailer

Updated 08/20/2025 | Published 12/01/2018

Products Featured in This Question

4-Pole Trailer End Connector

(38)

$8.12

Hook Probe Circuit Tester

(59)

$13.22

Question:

Uhual trailer I have a uhual hitch installed, the break lights and turning signals work but I was unable to rent the trailer due to the lights that turn on, on the side of the trailer for night time driving.

asked by: Felix P

Expert Reply:

If the running lights on the U-Haul trailer were not working when hooked up to your vehicle, then I first recommend testing the 4-Way or 7-Way (whichever you have) and testing the pins with a circuit tester like # PTW2993. Have somebody run through the lighting functions on the vehicle while you test the pins. If you don't get any power to any of the pins with the running lights activated, then you at least know the issue is somewhere on the vehicle and not on the trailer you hooked up to.

Inspect the connector itself for any debris or corrosion that needs to be cleaned out. Take a look at the wiring at the back of the connector for any exposed or pinched areas that need to be replaced. Also make sure the main harness ground is securely attached to a clean bare metal surface.

If everything looks good, I recommend checking your vehicle's owner's manual for the fuse locations to see if there is one for trailer running lights. If so, make sure this fuse is present and in good condition.

If you are still having issues, please let me know and we can continue to troubleshoot. I have also attached a trailer wiring troubleshooting article that you might find helpful.

expert reply by: Chris R

Joe

8/19/2025

I try all the fuses The daylight still don't work when I connect the trailer

Chris R.

8/20/2025

@Joe Hey Joe, I'd probably check the connector itself next (unless it's brand new) to see if there is any debris or corrosion built up that might be causing a short, brushing out as needed. Also, this is going to sound dumb...but make sure too that you actually have the running lights on in the vehicle. Let me know what you find.