Sorting the Electical Wiring in Your Trailer - Getting Wired

If you just can’t figure it out, the Tow Doctor plugs into the trailer wiring and diagnoses it for you. It’s a spendy piece of equipment, but if you tow a lot of weird stuff or have a business that requires a lot of towing, it’s worth the cost of around $200.

Electrical converters are used if you have the European standard lights on the tow vehicle. This is where it has amber turn signals instead of the regular U.S. system, where the turn signals and brake lights are red and are lit by the same bulb. If your Euro-spec rig doesn’t have an electrical plug already wired for a regular trailer, get a converter or none of the lights will work right, and you could damage your tow rig electrics.

Nearly any auto parts store or hitch installation center carries adapters for proper wiring. Even checking out the Web can lead you in the right direction for the right plug. This assortment alone could save you all sorts of time and trouble, and all it takes is a little searching rather than cutting and splicing a bunch of wires together.

Tapping into a vehicle’s wiring is a snap with T-connectors. Simply unplug the junction connector at the rear of the rig and plug the connector in between. Now you have a standard flat-four outlet with no guesswork as to what goes where.

Almost all new trucks with towing packages have gone to a six-round plug, and if you look in the glovebox it will probably still be there. Check your owner’s manual for wire color codes if you have to jiggy-rig this style.

Here’s the most common flat-four-wire plug. It’s quite simple really. Just like the round four-plug style, white is ground, yellow is left turn and brake, green is right turn and brake, and brown is taillights, marker lights, and license light.

Seems like every time we loan out our trailer it comes back with the lights not working, and we end up having to rewire the whole thing. It’s not that we did it wrong the first time, but with the multitude of different plugs, adapters, and tow rigs, a lot of custom jiggy-rigging of the wires always occurs.

You’ve probably done it yourself—connect bare wires into the trailer plug, attempt to figure out where they go on the vehicle, and hope you don’t short out and burn them both down. Well, guess what? There is a standard way to wire plugs and trailers, and almost every adapter is made to hook nearly any combo together!

It’s the law. You need to have lights on your flat-towed rig or trailer, and it’s simply unsafe not to comply, or have only half of them working. Wiring a trailer incorrectly means you may flash a left turn signal in the truck while the trailer indicates a right turn, which could have disastrous results. Check out our diagrams and products we’ve selected so you can do a proper wiring job. It may save you a ticket, or your life.