How to Wire Trailer Lights Correctly!

No matter how many pins and conductors your trailer has for lights, brakes, and accessories, there’s a correct way to route and connect all the wires. Learn where to get the right resources to do the job right the first time!

#trailerlights #wiringharness #trailerwiring

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At first glance, all the different colored conductors used to wire a trailer can be quite confusing. But, once you know what those colors mean, you are more than halfway there to getting your trailer wired correctly, without paying someone else to do it!

This episode is NOT about how to install wires, soldering, and basic electric connections. We’ve made the assumption you know how to do that. This episode IS about directing you to some GREAT resources for wiring diagrams, wire color designations, and wiring parts.

It bears repeating that doing a neat job, securing wires along the frame so they are not dangling, sealing connections to reduce corrosion, and assuring the system is well grounded to the trailer’s frame are ALL key to having trouble-free wiring for - pardon the pun - the long haul. The same goes for both the trailer’s connector (which has to be flexible), and the vehicle connector plug. These need to be sealed, and it’s MUCH better if the vehicle plug port is secured to the vehicle instead of hanging down.

Let’s begin with understanding industry-standard color codes for trailer wiring.

Green is for the right turn signal.
Yellow is for the left turn signal.
White is the ground.
Brown is for the taillights.

If that is all that your pull-behind trailer has, this is known as “four-way wiring.” It is very common and is widely seen on light-duty pull-behind utility and boat trailers.

Add one more conductor, and you now have a 5-wire setup. That 5th conductor is blue.

The four other conductors still do the functions mentioned earlier, but that blue conductor will now operate and control a trailer or camper’s “surge” (over-run) brakes. When the vehicle brakes are applied, the surge brakes come on as well to help assure the towed vehicle doesn’t “over-run” or push the towing vehicle.
The blue conductor is also tapped into the brake and backup lights so the trailer brake lights come on when the vehicle brakes are engaged, as well as disengaging the trailer’s braking system when the trailer is being backed up.

Six-way wiring adds a sixth wire (which is usually red) that can be used for various purposes. It can power a fused battery lead or a fuse block that other items are connected to, such as interior lights, fans, battery charger, or for electric brakes.

Seven-way wiring (purple) provides yet another power source for backup lights or a hydraulic coupler.

Each product you buy will have installation directions, but knowing what wires go to what devices or lights will make the whole system work correctly. That’s because the vehicle plug where you will connect the trailer is using the wiring convention just outlined.

As promised, here are some charts and diagrams you will find to be very handy:

https://www.waytekwire.com/AboutUs/The-Waytek-Blog/Terminals-and-Connectors/Trailer-Wiring-and-Connector-Basics#

https://www.etrailer.com/faq-wiring.aspxf

If you really want to “know your stuff” about trailer wiring and gear, check out this:

https://www.etrailer.com/faq-trailer-lighting-info-and-regulations.aspx?

Lastly, you should know that the VAST MAJORITY of trailer lighting problems occur because of poor grounding or non-grounding of the wiring harness. Electricity will always try to find a way to ground, including other components and bulbs. If the colored wires are wired to the correct items, and you still have problems, it’s likely a poor ground. If it’s not that, it’s probably a short somewhere where the insulation on a section of wire has worn through and is touching metal.

JUST DO IT YOURSELF!

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