Thursday, March 30, 2023


Setting up trailer light wiring

Steve Savage submitted this article to when he was a Master Certified RV Technician with Mobility RV Service.

Ehsnils on wikimedia commons

There are several common mistakes that often pop up when folks attempt to replace their plugs and receptacles that power their trailer lights and brakes.

The first mistake is pulling a wiring diagram off the Internet that designates wire colors. Owners often assume the colors on the diagram will match the wires on their truck or camper. You need to remember colors are irrelevant. What the wires do is important, not what color they are.

Anytime wires have been removed or come loose and left hanging, the prudent next step is to determine the function of each wire and write it down, then fasten the appropriate wire to the correct pin on the seven pin or cord. That way any arrangement can be wired to any plug.

The second common mistake we often see is that of forgetting to take note of the orientation of the wiring diagram that is being used. Sometimes the wiring diagram shows the receptacle from the back, sometimes from the front. Get confused and you will quickly discover things do not work right. The most common symptom is many lights going on at once when power is fed through the pin that should be the trailer ground.

If what you’ve just read makes sense to you, then go ahead and proceed with your own wiring. In the event it does not, I would suggest you are working over your head and would benefit by hiring someone to install your components, or ask a more experienced friend for help.




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2 years ago

I’m not understanding Steve’s explanations here. Like how wiring color isn’t important- just the function. I think they are both important. The wiring for boat trailers is universal….each color means a specific function. For instance, If you install a new pigtail on your trailer harness and connect mis unmatched colors, you’ll have problems. It could be that Steve is referring to the vehicle wiring- which could be different than the trailer….in that case his explanation might make sense. In the instance where a wire comes loose, just reconnect it to the spot it fell off of- pretty straight forward.

To RV Travel- Steve doesn’t return any email inquiries. Maybe you guys have a way of clarifying his article. 🙂

2 years ago
Reply to  Drew

I have to agree, there is a standard color code for trailers, unfortunately people don’t always follow it, and RV manufactures probably never do. I think he is just saying to be cautious and verify before making your connections,

2 years ago
Reply to  RV Staff

I was going to comment on how I have never seen a 7-pin layout as the image shows. But a search on Wiki (where the image was from?) and I see that style has been used. Typically the 7th pin is in the center.

2 years ago
Reply to  Drew

I think what he was trying to say is that the colors of the wires on the tow vehicle probably do not follow the colors of the wires in the trailer harness. And, of course, unless it’s a new trailer, and, sometimes even then, you have no idea what color wire was available to someone who was doing a repair on the trailer wiring or just wiring it.

2 years ago
Reply to  Drew

I think what he is saying is that you can’t trust the colors to be correct. I experienced this when restoring a 1976 Frolic several years ago. One of the previous owners had done some electrical work. The colors going to the trailer plug were random, no relation at all to the standard color scheme.

2 years ago
Reply to  Firefly


Thanks for the feedback!

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