Vehicle Electrical Hookups
When towing a trailer, it’s important to have electrical connections to the trailer for brake, turn, and position lights. This is most commonly, but not best achieved via a flat 4 plug. (read on for details)
With the advanced electronics on most modern tow vehicles, a trailer wiring adapter is required to transition the signals from the vehicle to the trailer. These are commonly available for most makes and models at auto parts stores. Some vehicles, especially if they have a factory tow package will already come pre-wired to the hitch, although you will have to provide the plug.
What’s the best plug to use? When connecting the wires between the trailer and the vehicle, a number of “standard” plugs are available.
There is the most common 4 wire plug that provides ground, running lights, left and right turn signal. The huge disadvantage of this plug is that continuous power (engine off) is not available to the trailer. It is very handy to have continuous vehicle battery power to the trailer for overhead lights, pumps, and other 12V accessories. It is also imperative to have brake power, if the trailer has electric brakes.
Because of these needs, six pin and seven prong connectors are also available. The fifth and sixths wires are 12V continuous and electric brakes. The seventh wire is generally an auxiliary 12V power wire that only runs with the alternator, commonly used for a trailer air conditioner.
The trailer wiring color “standards” are:
While the six pin connectors are quite a bit smaller than the 2” diameter seven prong connectors, I would suggest using the seven prong connectors. I wired our equipment with the six pin connectors and have had significant problems with corrosion of the pins and difficulty in disconnecting the plugs. The seven prong connectors also seem to be more common. If you have your vehicle hooked up with a seven prong connector, I would suggest grabbing one of the seven to flat four adapters and throwing it in the glove box. It’s always handy for those rental trailers, and helping a friend.
One other wiring trick is to wire an additional plug on the trailer with just ground and 12V power. With just two wires you can use heavy gauge lamp cord to create a far reaching cord so you don’t have to back the car or truck up to the trailer. Another way to extend the wiring is to create an extension cord with a trailer plug and receptacle to extend the existing plug. This method has the advantage of being stored inside the trailer, but has the disadvantage of getting lost. You may want to consider using three wires if you have auxiliary equipment that requires alternator power.