Semi Truck Hitch Wiring

So, you’ve got your trailer connected to your truck with the right hitch, ball mount and trailer ball. You’re ready to go, but what about your trailer lights? If the trailer connector doesn’t match the one on your tow vehicle, or if the vehicle doesn’t even have a plug, stick around. From basic exterior lights to 12-volt powered accessories, all trailers need electric power supplied by your vehicle, and we have everything needed to make a hassle-free connection including extensions, connectors, harnesses and adapters.

There are a number of standardized trailer connectors, such as 4-pin flat/round, 5-pin flat, 6-pin square/round, and 7-pin round. The simplest 4-pin system is used for small trailers, and has one ground pin, one pin each for left and right turn signals and brake lights, and one for the running lights. 5-pin flat connectors add a wire for the back-up lights. If the trailer is equipped with surge brakes, this circuit also disengages the brakes when the vehicle is backing up.

In addition to connections for turn signals, brake lights, tail lights and ground, 6-pin connectors have one terminal each for electric brakes and 12-volt accessories. 6-pin connectors come in square and round styles and are common to gooseneck and 5th wheel trailers, boat trailers and campers. 7-pin connectors are most commonly found on new vehicles that are prewired for towing. Along with the same functions as a 6-pin connector, this connector has a 7th circuit that is for the back-up lights. 7-pin connectors come with round or RV blade-style pins. Fortunately, no matter what connector you have on your trailer, we have the wiring harnesses that will let you plug into your vehicle’s electrical system.

The first thing you have to determine is whether your vehicle has a factory installed trailer towing package. If it does, you’ll find an electrical connector at the rear of the vehicle, usually on or near the bumper. If the shape and number of pins (wires) on the vehicle connector matches the one on your trailer, then all you’ll need is a wiring harness of sufficient length with the same connector at each end. If not, we can supply you with a plug-and-play adapter harness that will make all your trailer electrical functions work, without any cutting and splicing. For example, if your truck has a 7-pin round connector but your trailer has a 4-pin flat connector, one of our adapter harnesses will have you connected in minutes.

But don’t worry if your vehicle isn’t already set up for towing, we can still get you connected without much hassle. For most vehicles we offer a plug-and-play T-shaped harness (so called because it connects to both of your tail lights) that connects your vehicle lights to the trailer lights. If you have an obscure vehicle for which no T-shaped harness is available, we can still help, but some splicing will be necessary. And if your vehicle uses separate bulbs for the brake lights and turn signals but your trailer uses one bulb for both, we can supply you with a converter harness that will make the connection simple. We also have a large assortment of brackets, connectors, sockets, and anything else you need to get connected.