Troubleshooting Brake & Turn Signal Lights Alternating with Curt T-Connector Wiring Harness # C55325

Question

Question:

Hello, I have a 1994 Ford Ranger XLT 2.3 5spd 2wd Extended cab short bed. I bought the C55325 controller a few years ago and have had a problem since I installed it. First, this has been tested on several trailers and all of which have lights that work perfectly normal when connected to other vehicles. The problem is when I have the turn signal oneither side it works as normal, until I apply the brakes. When brakes are applied, brake lights illuminate on the truck and the trailer. However the turn signal flash on the truck and trailer begin to alternate with each other, only while the brakes are applied. When the turn signal on the truck is illuminated, the trailer turn signal is off, and vise versa. I was wondering if this may be a common issue related to a faulty module or a ground somewhere thats easily locatable. Any help is appreciated. Thanks for your time.

asked by: Zachary R

0

Expert Reply:

Hi Zachary,

From what you're describing that sounds like an issue with the module in the Curt T-Connector Wiring Harness part # C55325. The module in this wiring harness converts the separate light signals into a combined one on the trailer side and if the module has failed then the signals aren't being combined. What you're seeing with the lights is what happens when a continuous ON signal from the brake lights backfeeds and instead of the turn signal overriding the brake light on one side the turn signal voltage and brake voltage cancel each other out inside the module. To test it, you can use a multimeter or 12V test light on the truck's 4-way flat and hit the brakes while the turn signal is on. If the turn signal pin on the 4-way has a drop in voltage when the turn signal is on and the voltage jumps back up with the turn signal off, then the module is defective. The only solution for this would be to replace the failed wiring harness since the harness can't be taken apart.

What kind of trailer are you towing with your Ranger? And what kind of taillights does the trailer have (LED or Incandescent)?

expert reply by: Claire H

0

Scott M.

11/7/2026

My Ranger is a 1995 built in 1994. When I first hooked up the connector the lights didn't function correctly. The Curt unit was fine, I had bad grounds on two different trailers. With bad grounds, things back feed and strange things happen. Also, make sure the lights on the truck work properly with the Curt unit installed, and no trailer connected. I had the two filaments touching each other in a multi-filament bulb, and you didn't notice the problem until the trailer was hooked up. That one drove me nuts for a bit. Hope this helps with this issue, have a great day !

Claire H.

11/7/2026

@ScottM Checking the grounds is always a good idea when it comes to wiring issues. I didn't even think about the filaments in the bulb so that's a great tip! Hopefully we hear back from them, and they've tracked down the cause. I appreciate you sharing your experience to help others!

Zachary R.

11/12/2026

Hello, thank you for the reply! So far, I've towed 2 trailers. One being a 6x12 aluminum utility trailer with all LED lights, and the other being a boat trailer with incandescent lights. The boat trailer lights do seem dim when connected to my Ford Ranger compared to when connected to other vehicles. The utility trailer with led lights seems to have a normal brightness, assuming because the amp draw is so much less with LEDs. All the lights(running lights, brakes, turn signals, head lights) on the truck work properly when disconnected from a trailer with the Curt Harness installed. Final note, when connected to the trailer, the truck turn signal seems to develop a slight hyper flash situation when the turn signal is on ONLY once brakes are applied. Once brakes are released, the turn signal pace goes back to normal. As far as the filament issue in the bulb, how would I go about investigating this? Thank you.

Claire H.

11/12/2026

@ZacharyR Because the lights are dimmer on the trailer with incandescent bulbs, that indicates that the wiring harness is having issues with the higher power draw. LEDs don't have much of an amperage draw, so they would seem brighter/normal. But, incandescent require more power and the module could be struggling with the higher draw which is why the lights aren't as bright. It could also be that there's corrosion with the ground wire or in the 4-way connector itself. The hyperflashing when connected to a trailer sounds like an overloaded grounded circuit or a bad ground on the boat trailer side of things. Check the connections on the truck and boat trailer (including the grounds for the trailer's taillights) for corrosion and make sure the ground is on unpainted, non-rusted metal. Most trailer taillights are sealed, so I'm not sure you can check the bulbs without breaking the seal which would make the lights susceptible to water damage.

Zachary R.

11/12/2026

@ClaireH I would not be entirely shocked if the boat trailer having dim lights were due to a corroded ground or other poor wiring connection. But like I said, both trailers' lights function properly and plenty bright when connected to other tow vehicles. However, back to the main problem of the turn signal on the trailer and truck alternating opposite of one another. I will follow the instructions you provided in your first response and if the module fails then I will be replacing it. Should I have to replace the module or find another solution, I'll follow with an update stating such. Thank you so much for your time and expertise!

Claire H.

11/12/2026

@ZacharyR From everything you've described, it seems like its all coming back to the wiring harness. I'm hoping that replacing the harness will solve all the issues you're having.

Troubleshooting Brake & Turn Signal Lights Alternating with Curt T-Connector Wiring Harness # C55325

Products Featured in This Question

Product Page this Question was Asked From

Featured Help Information

Instructions

Continue Researching