How to wire a seven-pin trailer plug

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How to wire a seven-pin trailer plug
Travel trailers equipped with 7-pin plugs enable the tow vehicle to charge the trailer batteries. (Streamlined Motor Homes image by K. Geijer from Fotolia.com)

Seven pole travel trailer plugs enable tow vehicles to supply more than just brake lights, indicators and running lights. The additional poles on the trailer plug also include battery charging, electric trailer braking, and auxiliary power. There are two types of seven-pin plugs. Round-pin plugs have round holes in which pins are inserted. Flat-pin plugs have blades which connect to the tow vehicle plug through tension. Both types of plugs have poles which are wired in a mirror configuration when compared to the tow vehicle. This allows proper connection of the poles when the plug is connected.

Skill level:
Easy

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Instructions

  1. 1

    Pull the wiring harness to the front of the travel trailer. The seven wires should be labelled according to their function, or colour coded. Colour coded wires are not guaranteed to be correct. Check the wire connections to the travel trailer to confirm the accuracy of the installation, if possible.

  2. 2

    Hang at least 2 feet of trailer wiring from the front of the travel trailer near the hitch. The extra wire allows the vehicle to corner without dislodging the travel trailer plug.

  3. 3

    Open the travel trailer plug to allow access to the pole connections. Many plugs are held together with screws at the rear of the plug. Unscrew the retaining screws and pull the plug casing apart to expose the pole connections. Note the position of pole one from the back of the plug and note the locations of the remaining poles. The connection type -- clamp, screw or tension -- will depend on the manufacturer and model of the trailer plug.

  1. 1

    Connect the ground wire -- usually white and of heavier gauge than the other wires -- to pole position one. Position one, on a round-pin plug, is located directly under the keying of the plug. The plug key is the raised portion of the round-pin plug which allows the plug to be inserted only one way.

  2. 2

    Attach the black power cable in position two. When looking at the rear of the plug, position two is clockwise from the ground connection.

  3. 3

    Connect the remainder of the outer wires in a clockwise fashion, as viewed from the rear of the plug while attaching the wires. Position three is the left turn and brake wire, typically yellow. Position four -- directly opposite the ground wire on the other side of the plug -- is the reverse light wire, typically purple. Position five is the right turn and brake wire, typically green. Position six -- situated next to the ground wire -- is the tail and running lights wire, typically brown. The seventh wire, in the direct centre, is for the reverse lights. The reverse lights wire is typically purple.

  4. 4

    Connect the rear casing of the trailer plug. Insert the plug into the tow vehicle's plug port. Turn on the tow vehicle's engine and test the connections.

  1. 1

    Connect the ground wire -- typically white and of larger gauge than the other trailer wires -- to position one. Position one, on the flat-pin plug, is located in the first position counter-clockwise from the notch in the plug. The plug notch is used to only allow the plug to be inserted only one way into the tow vehicle's plug port.

  2. 2

    Attach the yellow left turn and brake wire to position two. Position two is located counter-clockwise from the ground wire when viewing the wires from the rear of the plug.

  3. 3

    Connect the remainder of the outer wires counter-clockwise from the left turn signal and brake wire. Position three is the brown tail and running light wire. Position four is the black 12-volt power wire. Position five is the green right turn and brake wire. Position six -- next to the opposite side of the notch where the ground wire is connected -- is the blue brake controller output wire. The seventh centre connection is for the purple reverse lights wire.

  4. 4

    Snap the rear casing of the trailer plug on the access point and tighten any retaining screws. Insert the plug into the tow vehicle's plug port. Turn on the tow vehicle's engine and test the connections.

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