Troubleshooting No Running Lights on Trailer but Turn Signals and Brake Lights Work
Updated 06/14/2024 | Published 01/01/2010
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Question:
I have a 4 way on my trailer w/ 5 wires and im plugging into a 4 way w/ 4 wires. I have brake lights and turn signals but cannot get the running lights to work.
asked by: John
Expert Reply:
The 4-way on your trailer is what's known as a wishbone connector like part # A35W42B. Two of the wires are the running light circuit which is a little easier to install since you can run one down each side of the trailer. This way you don't need a jumper wire to go from one side to the other. A wishbone 4-way is compatible with a standard 4-way, so your problem is somewhere in the wiring itself.
I would start by checking the 4-way on the truck with a circuit tester, like part # PTW2993. Testing the truck's connector tells if the problem is on it or the trailer. If everything checks out here, then the issue is on the trailer side. If you have a problem on the truck, then you need to trace the wires coming from the connector looking for any damage. You should also check the ground connection making sure it's clean and solid. It should be grounded to bare metal as well.
If the trailer is the problem, then start at its connector. Make sure the pins are clean and corrosion free. Then you want to inspect the running light wires throughout the trailer. They're traditionally brown wires but may not be. Since you have two, they'll be the second and third wires starting on the side with the ground pin. Take a look at the picture I attached. Check for any damage or pinch points. You should also check the ground connection on the trailer side as well.
Kb
4/20/2020
I have retired the entire trailer and have turned the lights on in the truck and still can’t get the running lights to work. If your tail light has 3 wires - red, white and black. What should they be hooked to on a 4 pin? I have the black to the brown, the red to green/yellow and white as ground? What am I doing wrong?
Chris R.
4/22/2020
Kevin S.
4/23/2020
I have turn and break lights, until the point that I turn the head lights on. Then there is no lights at all that work on the trailer. So the result is, no running lights at all on the trailer side. Only have tail lights for the trailer, as long as the headlights are off on the truck. I checked the running light pin on the truck plug, and I do show it is getting power to it.
Chris R.
4/24/2020
Kevin C.
6/14/2024
Pedro J.
5/2/2020
I just bought a trailer light kit, everything works except for the left break light all wires are new and fine all connections fine I’ve put 2 different brand new bulbs in one led one regular and changed the plug on the trailer end. I have several other trailers and this is the only one that does this any ideas
Chris R.
5/5/2020
Todd B.
5/18/2020
I added side marker lights to my new trailer. when it is plugged into my truck still do not work. I can hook it staight to my battery and they will work. I tried even to run hot wire to them and grounded it on truck still doesn't work.
Product Page this Question was Asked From
35 Ft 4-Way Trailer Wiring Harness - Wishbone Style - 42" Ground
- Custom Fit Vehicle Wiring
- Trailer Hitch Wiring
- Vehicle End Connector
- No Converter
- Universal Fit
- 4 Flat
- Plug and Lead
- Splice-In
- Optronics
more information >
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Cameron
3/1/2020
Im not sure how old this thread is but its near the tip of the search for this question still so here goes nothing. I just got done rewiring my whole trailer because I had this very same issue. No running lights, but brakes and turn signals worked. You know what the problem was?... Hanging my head in shame... I wasnt turning the lights on in my car...