Running a 12 Volt Trailer Connection Circuit on a 2007 GMC Classic Body Style with a Diesel Engine

Expert Reply:

There is a power distribution box under the hood of the 2007 GMC Sierra that has two power posts that can be used for power to a brake controller and 12 volt power to the 7-Way RV connector at the rear of the vehicle.

If your truck is equipped with a factory 7-Way and the 12 volt power circuit is not functioning you will need to check the 40 amp fuse nearest the forward most power post in the power distribution box. See photo at right.

If you do not have a factory 7-Way on your vehicle or the wiring is not completed to the forward most power post you will need to run a 10 gauge wire, item # 10-1-1, from this power post to the 7-Way at the rear of the vehicle. A 40 amp fuse will be needed in the location nearest the power post. These are available at any local auto supply. I have linked an article that shows where the power connection should be made in the 7-Way connector for you to review also.

The 12 volt circuit for charging the trailer battery will not charge a depleted battery fully but is designed to maintain a fully charged battery while the vehicle is running. You will want to use a battery charger, item # CTEK56158 would be a great choice, to fully charge the trailer battery before trips. Once fully charged the power wire from the 7-Way will help keep the battery fully charged for times when shore power is not available.

You will want to disconnect the trailer connector when not towing to avoid draining the vehicle battery. If this is a concern you can install a battery isolator, item # TR118665, inline with the power wire, to eliminate the possibility of draining the vehicle battery when the vehicle is not running.

expert reply by: Bob G