How to Make a 9 Pin to 7-Way Adapter for Connecting Semi Truck to Trailer

Published 10/20/2015

Products Featured in This Question

7-Way Round RV Style Trailer Connector - Trailer Side

(361)

$11.92

12 Gauge 7 Conductor Jacketed Wire - Per Foot

(502)

$9.55

Roadmaster Brite-Lite 3-to-2 Tail Light Converter for Towed Vehicles

(115)

$61.92

Question:

I own a 2008 k.w. T660 semi that i run over the road with, I just bought a 40foot 3 axle fiver, to place at my west coast turn around seattle so, i have homes to spend time at on both ends of my run. My question is, as i still use my trk for business. So, i cannot modify the actual pigtail What would be the best way to adapt my comm. Trk pigtail To work with the 7 blade on the trailer, and still have the elec brakes on the trailer either work or stay released as im fairly sure my truck has enough stopping power on its own. 500hp, 2000 ft tq, 3 stage jakes, 18,500lb tractor, And do i really need a elec brake controller in the truck? I still have a spare P3 at home?

asked by: Mike

Expert Reply:

I have a solution for you that will allow you to make an adapter, but we do not sell one pre-made.

To adapt your 9-pin trailer plug to work with the 7-way connector on the truck, you would need the 9-pin vehicle side connector that you referenced, part # R9CB. A length of 7-wire cable # DW04914-1 from the 9-pin would be tapped into the relevant circuits behind the 7-way, with the two remaining terminals being connected as needed. For a more temporary install, the 9-way R9CB could be temporarily attached to the truck, with a length of # DW04914-1 wired to the appropriate terminals on the rear of the connector. Wire the other end of the cable to a 7-way trailer end like # A7WCB, which would plug into the 7-way on the truck when needed. The remaining two terminals on the 9 pin would be connected as needed.

I attached a diagram that has a chart with how a 7-way typically gets wired up. To determine the functions of the pins on your 9-way you would need to use a circuit tester like part # 3808 to test each of the pins.

If your trailer has combined turn signals from the brake lights and your truck has separate then you would also need to use a signal converter like part # RM-732.

Most likely you will need to activate the trailer's brakes so an electric brake controller like the P3 # 90195 would be an excellent option. I attached a help article on how to hardwire this controller in.