Installing a 7-Way Connector at the Rear of a 5th Wheel Trailer with a 4-Pole Connector

Updated 01/13/2025 | Published 08/23/2017

Products Featured in This Question

Adapter 4-Pole to 7-Pole and 4-Pole

(663)

$31.52

10 Gauge Wire - Blue Primary - Per Foot

(104)

$1.75

12 Gauge 2 Conductor Jacketed (Brake) Wire Per Foot

(511)

$2.73

No-Drill Mount for Electrical Mounting Bracket - Short

(1183)

$24.05

Deka Heat Shrink Butt Connector - 12-10 Gauge - Nylon Insulation - Yellow - Qty 5

(1110)

$7.45

Question:

I need to pull a trailer behind my 5th wheel. Double pull. My fifth wheel has a 4 pin at the rear but my trailer with electric brakes is a round 7 pin. I pull with a 3500 Chevy Duramax. Can I convert the 4 pin to 7 pin at the back of the 5th wheel. What would I do to have the electric brakes work on the second trailer? Can I just tie into the brake wires on the fifth wheel trailer which would then utilize the truck brake system? Not sure if both trailers would brake evenly.

asked by: Brett B

Expert Reply:

To get a functioning 7-Way at the rear of your 5th wheel trailer that has a 4-Pole you will want to install the Adapter 4-Pole to 7-Pole and 4-Pole # 37185 which can be mounted to your bumper using the No-Drill Mount Bracket # 18140. To get the 12V Power and Brake Controller signal from your Chevy Duramax you will then need to run Jacketed 2 Wire (Brake Wire) # 12-2-1 up to the 7-Way on your Duramax and splice it in. If Butt Connectors are needed use part # DW05745-5. If the Auxiliary pin (Purple Wire) needs 12V power then you will want to use 10 Gauge Wire # 10-1-1 to run any additional wiring.

Since all of this wiring will be drawing off of the 7-Way on your Chevy you might experience some electrical failures due to the increase in draw power.

Please keep in mind that in most states it is illegal to pull 2 trailers at the same time. You will want to check local laws of any cities you will be passing through to make sure that you are staying compliant with the law.

expert reply by: Jon G

Felix S.

1/12/2025

I plan to do the same, I f I get a y splitter in my bed of my truck and use one for the fifth wheel and the other for my utility behind my fifth wheel and run a 7 pin back all the way to my trailer in the rear, will I burn up the rear brakes on the utility trailer behind my fifth wheel? Do I need to add a whole new 2nd brake controller and set it to a lighter setting then my fifth wheel?

Jon G.

1/13/2025

@FelixS Possibly. Brake controllers are rated for X amount of brakes so something like the Prodigy P3 # 90195 that can handle up to brakes on 4 axles wouldn't have enough power for a triple axle 5th wheel and a tandem axle trailer behind that. To be honest, a lot of this is going to be experimental on your end. We don't advise double towing so there's a lot of questions I simply don't know the answer to. What I would do is try with your one controller and take your whole towing rig to an empty parking lot and test out how the brakes perform. Worst case scenario is that you have to install another brake controller on your 5th wheel, and at that point you either need something like the Prodigy RF # TK94FR, or you'll need to install a regular brake controller and the Universal Stop Light Switch Kit # RM-751000 to get your brake light switch signal for the brake controller.