Curt 4 Flat Trailer Wiring only Getting 4-5 Volts When Testing Blinker Output.

Updated 12/15/2025 | Published 11/25/2024

Products Featured in This Question

Curt 4-Way Flat Trailer Connector with Circuit Protected Powered Tail Light Converter

(60)

$34.85

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

(14)

$81.25

Question:

Pretty sure I know the answer here but this issue is just strange. I have a 4 way flat output for my honda fit I got about 2 years ago and initially it was working fine. Fast forward to today and I go to use it again and putting a tester on it lights all three lights solid with the break line being brighter. Putting a meter on them I get around 12 on the break lights and 4-5 on the turn lights. No change to turn signal or applying breaks, always on as well even when car is off. Connecting to trailer just gets strange. Harbor freight trailer so the problem could be with the crappy harness for sure, but when I seemed to get my ground issues fixed the only lights that come on are the side lights. Initially when I first connected the last ground the tail/break lights came on, but when I fiddled around and rest them to test he turn signals they went out and have not come back on since. The front left and right side light are on, the rear left and right sidelights are on BUT dim... unless I disconnect the ground to the front left side light.... and heres the kicker. Even with all grounds disconnected if I test with a meter from any of the power leads to the lights and touch it to the frame I get 4-5 volts........ the trailer is isolated, on tires but not hooked up, hitch and chains on a foam cooler. Well to start Im pretty sure the controller box is hosed. The behavior even without the trailer seems to indicate that.

asked by: Greg

Expert Reply:

Hello Greg.

The first thing I would suggest to do is to check the ground, but it sounds like you already did that. When you tested the voltage of the blinkers, were the blinkers on (green wire, right turn; yellow wire, left turn)? You should be getting about 12 volts, not 4-5. Sounds like the brakes (red wire) is working just fine at 12 volts. If that is the case, you definitely have a bad converter (controller box). Unfortunately, these do go out. The Curt 4-Way Flat Trailer Connector with Circuit Protected Powered Tail Light Converter # C56496 has a 1 year warranty, so if you purchased it 2 years ago you would be outside of that. If you are going to replace the wiring, I would suggest going with the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118767. This wiring is vehicle specific and installs through the connectors in the back tail lights. When it comes to the wiring, I usually go with the Tekonsha over the Curt. Curt's an excellent brand and I do love their hitches, but when it comes to the wiring Tekonsha is the superior brand in my opinion.

expert reply by: Kate F

Kate F.

12/15/2025

Hey Greg, how did things turn out after you replaced the controller box on your Honda Fit? Did the new wiring harness clear up the strange voltage readings you were seeing? Your update could make it easier for others troubleshooting similar trailer light issues.