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Hardwiring in a Trailer Brake Controller on a Ford Expedition

Question:

Can you help me with where to run my wires for a brake controller inside, under the dash. My expedition seems to be one of the few not wired with a factory plug. I have all the right wires at the back where it originally had a 4 pin connector. I have put in the 7 pin in already.

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Expert Reply:

Since you are hardwiring in a brake controller you can start with the white and black wires. The white wire is ground and needs to go to the negative battery terminal. Black is power and it needs to go to the positive battery terminal via a 30 amp circuit breaker. For this you can use wire # 12-2-1, sold by the foot. There are 2 wires inside and you can use 1 for ground and one for power. For a 30 amp circuit breaker use # PK54530.

The wires will need to be run through the firewall. This includes a third wire (the one that goes back to the 7-Way). Look for other wiring that goes through the firewall. If you can't access it then you will need to drill a small hole, run the wires through, and seal up the hole with silicone. If you drill then be careful of what is on the other side of the firewall!

Next you will need about 20 feet of wire # 10-1-1 sold by the foot. This will go to the brake controller blue wire, through the firewall, and attach to the blue wire from the 7-Way you installed or, if it doesn't have wires, it will attach to the back of the 7-Way in the 7 o'clock position.

That just leaves the red wire on the controller. It attaches to the cold side of the brake switch. Use a circuit tester such as # 40376 to test the brake switch wires (located above and often attached to the brake pedal arm). Probe the wires until you find the one that only has power when the brake pedal is pressed. If it has power with the headlights or turn signals on then it is not the correct wire.

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