Although a seven-pin -- sometimes called seven-blade -- tow packet plug by definition has seven wires in its loom, lone two are related to the servicing of the brake controller. One of these is the white wire, from the plug to the trailer ground, and the other is the blue wire, from the plug to the electrically-actuated magnets which deploy the brakes themselves. Diagnosing a brake controller problem within the seven-pin plug itself is thus a simple and quickly-accomplished project.
Instructions
1. Use your screwdriver to remove the fastener or fasteners securing the inner and outer components of the seven-pin trailer plug and separate the two parts. Visually inspect the connections to the terminals color coded to attach the white and the blue wires. A poor connection at the terminals may be due to a loose terminal screw or a frayed wire. If the visual inspection and voltage meter tests of the seven-pin trailer plug does not reveal the cause of a problem with the brake controller, use a voltage meter to test the outlet and loom of the tow vehicle.6. If the visual inspection and voltage meter tests of the seven-pin trailer plug and the voltage meter test of the outlet and loom of the tow vehicle does not reveal the cause of a problem with the brake controller, use the voltage meter to test the loom or equipment of the trailer.
Test resistance across the pin attached to the white wire, from the pin itself to the wire. If there is continuity repeat the test on the pin attached to the blue wire. If either pin test reveals a lack of continuity, rewire that pin.
3. Rewire a pin connection by cutting off the already-exposed wire, then using your wire strippers to remove the first half inch of insulation. Twist the newly-exposed wire into a taut, rope-like braid and insert it into the circular hole in the top of the pin. Tighten down the pin's securing screw until the wire cannot be moved.
4. If the visual inspection and voltage meter tests of the seven-pin trailer plug does not reveal the cause of a problem with the brake controller, the problem may be before the plug, in the outlet or loom of the tow vehicle. It may also be after the plug, in the loom or equipment of the trailer.
5. Use your screwdriver to tighten a loose terminal screw. Rectify a frayed wire by removing the wire end from the terminal and twisting the separate strands into one firm, rope-like braid, then remake the connection by inserting the braided wire into the terminal receiver and tightening down the screw.2. Calibrate a voltage meter to the manufacturer's instructions for 12 volt systems.
