How to Bypass Smart Tow Feature of Ford Trailer Wiring for 12 Volt Accessory Circuit

Updated 04/30/2025 | Published 07/02/2020

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10 Gauge Wire - Blue Primary - Per Foot

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40 Amp In-Line Circuit Breaker - Perpendicular Mount Bracket

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Question:

Hi Jameson. Read several of your responses to similar issues to the one we have with our brand new 2019 Ford F450 ... we have 3 trailers, all of which have some accessory a hydraulic jack, interior lights, etc. that require 12V accessory power from the rear 7-pin plug ... however, Fords TRM smartinch system requires there to be a trailerinch plugged in, the door shut, the ignition on, and either the vehicle moving or the brake pedal pushed the answer varies from different Ford technicians and service managers ... which doesnt make sense with a trailer jack, for instance. You mention using a 10-gauge wire and a breaker to bypass this ... could you be more specific? Im not terribly mechanical...: 1 run the wire part # 10-1-1 from which pin 2019 F450 .. .which of the 7-ways is the 12V pin?, 2 through the breakerinch part #9510 ... what does that mean exactly? the breaker appears to have two posts how do i attach, to which or both, etc.... before running the wire to the ... 3 ... positive post of the battery Finally, is this something an independent mechanic could/can/would do? Im not all that nimble to be crawling around under the truck anymore... Any help appreciated!!

asked by: Matthew M

Expert Reply:

I can definitely help be more specific with the instructions I've mentioned on bypassing the 12 volt accessory pin on your Ford truck. So basically what you'd do is take a length of 10 gauge wire like # 10-1-1 (sold by the foot) and connect it to the 1:00 pin position of the 7-way. This is the 1:00 pin as you face the opening of the connector, and then connect the other end to one of the posts on a breaker like part # 9510 and then run wire from the other post of the breaker to the positive terminal of the battery. This isn't overly difficult or complicated but it will require you to get under the truck to route the wire from the rear of the truck to the front.

A local mechanic would have no problem pulling this off as well. This would be a very simple job for them compared to some of the other jobs they have to do on a regular basis.

expert reply by: Jameson C

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Jason

4/30/2025

When you do this accessory bypass, do you but the wire that is coming from the factory harness to the 12v PIN on the 7 way plug ? I can see offering 12v from the smart switch (Truck) and then also offering your own 12v from the 10gauge wire to the back could be a problem. I also dont want to the computer to think something is wrong if I cut the factory orange wire that connects to the 12v pin on on the backside of the plug. I want to wire in my upfitter switch which has the fuse inline already and would be super easy to do, and allow me to keep my trailer accessories and batteries topped off while rolling (frig too) which would be key on long pulls. Thanks in advance.

Jameson C.

4/30/2025

@Jason Hey Jason, yes you would run the 12 volt wire to the 12 volt pin of the 7-way. You would disconnect the current 12 volt accessory circuit that is there now and run this as the only source for it. This wouldn't cause any computer issues as long as you tape up the wire you disconnected.