If you are new to the trailer world, or an old pro looking to refresh your memory, keep reading to learn about the most popular trailer plugs that are used today.
Lets start from the smallest, or at least the plug with the fewest functions. The plug in the picture below is commonly referred to a flat 4 plug.
This plug is common on most single axle trailers, and performs the basic functions needed to tow a trailer, lights. This plug is for the stop, turn signal, and taillights, and also the marker or running lights. Now I say that this is most common, and not the standard, because there are a few other possibilities. Some single axle trailers, mainly in the boat trailer industry, have a flat 5 plug, but not as common as the 4.
Next on the list is the round 6 trailer plug. This is for a trailer that has electric brakes, therefore it is a little larger to accommodate the other functions. Below is a picture of the round 6 trailer plug.
This plug if for the normal light functions of a trailer, with the added brake wire to operate the electric brakes on the trailer. There are 2 ways to wire this plug, and there is no standard way that the trailer manufacturers do this. The brake wire can be wired to the center pin, or the outer pin. If you have a 6 way on your tow vehicle, you will need to make sure that the brake wires match in order for them to function properly. If you have a newer vehicle that comes with a factory 7 way plug (we will get that in the next photo) there are adapters for that to be able to tow a trailer with a round 6 plug. Once again, since there are 2 ways to wire it, there are 2 different adapters. One will work beautifully, the other will lock up those brakes.
Next is the most common larger plug for trailers. This is referred to as a 7 way RV style plug. Below is a picture of what the trailer plug looks like.
This is a common plug on most tandem axle trailers currently made today. It matches up to most factory OEM plugs on newer vehicles that come with a tow package. Functions are the same as above, with the one difference that there is one way to wire it. No need to worry about it matching up with a factory plug on your vehicle. There is one slight thing that may not match up, and that comes to play when towing a dump trailer, or a trailer with a battery. The 12 volt wire may or may not be hot on your tow vehicle, or connected in the trailer plug. A tester can be used to determine if it indeed is hooked up. The 12 volt wire is used to trickle charge a battery, i.e, on a dump trailer. Regardless, the lights and electric brakes will work with or without that wire being hot.
Last but not least, is a trailer plug that is referred to a round 7 way tractor trailer style. This plug is most commonly found on larger trucks, mainly semi trucks, and tow trucks, for instance. Below is a picture of what a round 7 tractor trailer style plug looks like.
This plug functions the same as the 7 way RV style, but is built a bit heavier for the use on the larger trucks that tend to tow daily. Lights and electric brakes are all operated and controlled through this style plug.
I hope this helped clear up the differences in trailer plugs that are out there, and I hope I didn’t confuse anyone either. When shopping for a trailer, be sure to check that your vehicle is first off capable of towing what you are looking at, and second, equipped with the right plug to do so.