Installing a 7-Way Trailer Wiring Harness on a 2003 Dodge Ram 1500

Expert Reply:

First, I would be certain that your 2003 Dodge Ram 1500 uses a 24 system. If you have 2 batteries and the positive of one is connected to the negative of the other, then it is a 24 volt system. But if the positive of one is connected to the positive of the other (and the same for the negatives) then you have a 12 volt system.

If you do have a 24 volt system what you would need to do to get power to the 7-Way would be to splice in a wire to the cable that goes from the positive of one battery to the negative to the other battery. At this point it is 12 volts.

Then attach that wire to the BAT post of a 40 amp circuit breaker, # PK54540. Then connect a wire to the AUX post on the breaker and route the other end to the black wire on the 7-Way.

If the truck came with a 4-Way flat connector, you would plug it into the 4-Way on the 7-Way adapter. Ground the white wire to the truck frame. The loose yellow wire would go to a reverse light wire on the truck.

The blue wire for the trailer brakes does not run all the way back to the trailer connector; it stops at the connector that is located under the driver side wheel well. In order to finalize the installation you must splice into this wire and continue it back to the plug and attach to the blue wire.

If the truck did not come with a trailer connector of any kind, you will first need to add a 4-Way using # 119175KIT (instructions linked). But, check the tail light wires with a multimeter first, # BTMT15, to see if the lights works on 12 volts or 24 volts. All of the 4-Ways for your truck work on 12 volt systems.

Then you can install # ETBC7 which comes with all the wiring and accessories you will need for installation. I have included links to an FAQ and video on installing an ETBC7.

expert reply by: Michael H