Boat Trailer Wiring Harness Considerations

All You Need to Know About Wiring a Boat Trailer

A boat trailer wiring harness is the device that links your car or truck's electrical system to the electrical component of your trailer. Appropriately wired, the trailer brake lights, tail lights, marker lights, turn signals, and trailer clearance lights will illuminate when you initiate these actions while driving your vehicle. Of course, this allows other drivers to see your boat trailer lights even with your trailer blocking your vehicle's indicator lights. Trailer lights are not only common-sense safety devices, but they are also the law.

So which wire harness do you need? Also, if you are revamping your boat trailer wiring, the following should offer some food for thought. When thinking about your boat trailer wiring harness, there are three things to think about: type of plug/socket, number of pins on the trailer wiring harness, and wiring configuration.

Trailer Wiring Harness Plugs and Sockets

Plugs and sockets are the connectors that allow you to plug your trailer into your vehicle. The shapes of the plugs and sockets vary, but flat, round, and RV blade are the most common options.

Flat

On flat connectors, the pins line up in a row.

Round

These connectors are round, with the pins arranged in a circular configuration. On six-pin connectors and higher, there's also a pin in the middle. Round outlets and plugs also have round pins and holes

RV Blade

RV blade connectors are round, with the pins arranged in a circular configuration. On six-pin connectors and higher, there's also a pin in the middle. RV blade plugs and outlets have rectangular pins and holes.

Number of Wiring Harness Pins

The most common trailer connectors have four, five, six, or seven pins. The more pins in the connector, the higher the number of functions it can handle.

Four-Pin and Five-Pin Wiring Harnesses

One pin is a ground on every connector in a trailer frame, so a four-pin connector will facilitate three functions. A five-pin connector will allow four functions. A four-pin connector is the most basic controlling turn signals, brake lights, and taillights—the lights needed for safety and required by the law. Upgrade to a fifth wire, and you add either backup lights or electric brakes, depending on the plug.

Standard wiring color code for a four-pin connector:

Ground = white

Tail/running lights = brown

Left turn/brake = yellow

Right turn/brake = green

Six Pin Wiring Harness

A six-pin trailer wiring connector allows you to add a 12-volt connection, which is more about convenience than safety. The sixth pin is a "hot lead" that will enable you to charge a battery in your trailer. Boaters generally don't need this sixth pin, but it comes in handy if you are towing a camper. All you need to do is plug the adapter into the tow vehicle connector and plug in the trailer tongue. Here, the full-length plug shell ensures positive latching.

Seven-Pin Wiring Harness

The seventh pin allows you to add yet another capability. Like the six-pin wiring harness, generally not needed by boaters, but convenient if you are hauling a camper or something of that nature.

Wishbone Wiring Harness or Crossover Wiring Harness?

Most boat trailers are configured with a wishbone wiring harness or a split Y harness that splits the running light circuit at the trailer connector so that you don't have to run a jumper wire from one taillight to the other.

The yellow/brown wire is the running light circuit for the driver's side. The green/brown wire is the running light circuit for the passenger side. Either wire will operate the running lights for the trailer; they are split to make it easier to wire to the taillights.

Less commonly, your trailer may be wired with a crossover wiring harness as the main harness. This wiring configuration means that the wiring runs down one side of the trailer and across between the taillights.

Frequently Asked Questions About Boat Trailer Wiring Harness

What gauge wire should be used for trailer wiring?

When it comes to the trailer light wiring, 16-gauge wire is generally recommended for a 4-pin harness or a 5-pin harness. However, for a 6-way or 7-way trailer connector, a minimum of 16-gauge for the turn signals, brake lights, reverse lights, and running light wires. The suggested minimum for the ground wire, brake power, and battery hot lead wires is 12-gauge.

How can I reduce the instances of faulty lighting?

Faulty trailer lights can often be caused due to a weak ground; hence it is important to ensure that the ground on the tow vehicle is connected to a plain, unpainted surface on the chassis. Moreover, each light assembly should be grounded to the trailer.

What is the use of a wiring harness in towing a vehicle?

The trailer hitch on your tow vehicle allows you to tow a trailer, but you need a wiring harness to power and appropriately control the lights on the trailer - turn signals, brake lights, running lights, etc.