How to Wire an Electric Brake Box for a Trailer
- 1). Insert the dedicated connection harness into the receiver at the rear of the electric brake box.
- 2). Route the blue wire of the connection harness through the tow vehicle to where the tow package is fitted at the center of the vehicle's rear quarter. Remove the case of the seven-pin hitch connector, usually fitted adjacent to the tow package, and attach the wire to terminal five. Replace the case.
- 3). Run the black wire of the electric brake box brake controller harness to a 12-volt connection, which is permanently live when the vehicle is switched on. The headlamp switch hot wire is usually conveniently close by in the dash. The harness kit should be complete with a cable splicer to make this connection, and an inline fuse holder with a fuse supplied by the manufacturer.
- 4). Locate the brake light microswitch under the dash close to the brake pedal pivot; it should be connected to the rear part of the pedal by a small spring. Use a voltage meter to identify which of the two wires attached to the brake light microswitch identifies as permanently hot when the vehicle is switched on, then attach the red wire of the electric brake box harness to the other.
- 5). Tie the white wire of the harness into ground, sharing a factory-installed bolt or screw already driven into the firewall below the dash.
Source...