What are the Different Types of Trailer Plugs & Which Do I Need?

The variety of trailer connectors available can make deciding on the right one for your trailer wiring difficult. While they all offer four basic functions, as we move into higher numbers of pins, which range up to seven, they offer additional functions.

Today we're going to break down the significance of different pins and their numbers so you can choose the appropriate one for the functions of your towed vehicle.

Types of Pins

You will encounter two different kinds of pins when it comes to plugs for your vehicle sockets: flat and round or RV blade.

Flat - Typically, flat pins are used for more basic trailer wiring. The pins will be lined up in a row and will typically only be used for four or five-pin connections which are used for towing smaller loads that require fewer functions.

Round pins/RV Blade - The shape of the plug and outlet for these pins are the same, but the shape of the holes and the pins will change. Round plugs are round, while RV blade pins are square.

Both plugs arrange their pins in a circle with six pins and have one in the center. They can come in four and five-pin counts though typically, this pin shape is reserved for larger loads requiring additional functions.

Number of Pins

Every plug has one pin, which is used for ground, meaning that each plug type will perform one function less than the number of pins the plug has.

Four-way Connectors

Four pin plugs, regardless of pin shape, only serve three lighting functions. The color coding of the wires for a four-pin plug is as follows -

• White - Ground
• Brown - Running lights
• Yellow - Left indicator & brake lights
• Green - Right indicator & brake lights

These plugs are available with round and flat pins, with the round pins providing a more robust connection.

Typically these are 20 amp pins though there are heavy-duty 35 amp round pin versions that aren't compatible with 20 amp plugs though the pins are the same size, so make sure you're purchasing a compatible plug.

Five-way Connectors

These offer the same three lighting functions as four-way connectors with an extra function for electric brakes or reverse lights depending on the trailer. The color coding is as follows:

• White- ground
• Brown = Running lights
• Yellow - Left turn signals & brake lights
• Green - right turn signals & brake lights
• Blue - electric brakes/reverse lights

Five-pin plugs come with flat pins though these are known to become easily corroded or have loose connections.

Round pin five-way connections provide a more solid connection and are popular with RV drivers who are towing an extra vehicle that they need a coach signal line for or for trailers with surge brakes.

Six-way Connectors

These plugs cover all the previous lighting functions of a five-way with the addition of a 12-volt connection, known as a hot lead.

The hot lead charges the battery in your trailer, so it's not necessary if you're towing a boat or carriage that doesn't need a battery but is helpful if you're bringing a small camping trailer along.

The color coding for six-way connectors is -

• White - ground
• Brown - running lights
• Yellow - left turn signal & brake lights
• Green - right turn signal & brake lights
• Blue - electric brakes
• Black - 12v Power/hot lead

Six-way Square Connectors

These deserve a special mention as they are particularly rare, and finding an adaptor for them can be very tricky. They're commonly used for small camper vans, providing all the same functions as standard six-way plugs with the following color coding -

• White - ground
• Brown - running lights
• Yellow - left turn and brake signal
• Green = right turn and brake signal
• Blue- electric brakes
• Black - 12v power

Color codes can vary on square connections depending on trailer manufacturers, but this is the most common configuration.

Seven-way Connectors

These are the most common form of trailer connection found in modern trucks, RVs, and SUVs, supplying all the same functions as the previous connectors, with the seventh supplying power to auxiliary or backup lights.

The wiring code for seven-pin plugs is -

• White - ground
• Brown - running lights
• Yellow - left turn signals & brake lights
• Green - right turn signals & brake lights
• Blue - electric brakes
• Black - 12v Power
• Orange/Red - backup lights

These are typically found with flat pins, especially in modern trucks that are equipped with a trailer hitch, and although seven-way round pin plugs can be found, they are uncommon.

Coiled Cables

Coiled cables provide the same function as four, five, six, and seven-pin plugs; only the cables are much more robust. Straight cables are prone to hanging loose, sometimes dragging on the road between your vehicle and trailer.

With this sort of loosely fitted setup, it might not be long before the cable is worn away and you lose all functionality.

Coiled cables are a reliable, longer-lasting alternative that can be purchased with both flat and round pins.

What Type of Trailer Plug do I Need?

The number of pins is directly proportional to the number of functions the plug supplies, which is an indication of which plug you need. If you're towing a smaller motorhome behind your vehicle, you will benefit from more pins, which is more common in the current market.

However, if you're simply towing a rig that's carrying other items, like bikes or a boat, you'll only need the basic four-way plug.

Another important consideration is where the connector is located on your vehicle. If the connection is underneath your vehicle, you may want to consider using a mounting bracket to avoid bending the cable, which will wear out the connection more quickly.

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