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Author Topic:   Trailer-Vehicle Connector Wiring
jimh posted 05-17-2008 07:59 PM ET (US)   Profile for jimh   Send Email to jimh  
I got tired of looking around the net for this information, so I wrote this reference article primarily to give myself a handy place to find it:

Trailer–Vehicle Connector Wiring

jimh posted 05-29-2008 09:24 AM ET (US)     Profile for jimh  Send Email to jimh     
In several on-line discussions I have noted that some new vehicle owners report that the 7-pin RV style trailer connector provided as part of the original equipment on their newer vehicles did not have the back-up light circuit wired to PIN 7 (the center pin) of the connector. This circuit is generally used on boat trailers which have hydraulically actuated disc brake systems in order to operate an electric solenoid that controls a valve in the brake system. The valve spoils the brake pressure from a surge actuator that occurs when the trailer is backed up. Unlike the usual free-backing drum brakes, disc brakes work as well in reverse as in forward.

I would be curious to hear reports from anyone with an OEM installed 7-pin RV style trailer connector on their vehicle as to whether or not it was wired with the back-up light circuit included and wired to the center pin (PIN 7). Give the model and model year of your vehicle.

newt posted 05-29-2008 10:27 AM ET (US)     Profile for newt  Send Email to newt     
My 2005 Ford F150 with tow package works as it should with my disc brakes.

I don't know which pin the backup light is mapped to, but an off the shelf 7-pin to 5-pin adapter works just fine.

andygere posted 05-29-2008 11:07 AM ET (US)     Profile for andygere  Send Email to andygere     
2004 Suburban 2500 QS
Factory installed Class IV towing package
7 pin connector includes reverse light contact.
Marlin posted 05-29-2008 05:02 PM ET (US)     Profile for Marlin  Send Email to Marlin     
My 2004 Ford Explorer with tow package has a 7-pin round socket under the bumper, off-the-shelf 7-round-to-5-flat adapter, and the brakes are disabled in reverse. Ford conveniently molded the pinout right into the socket cover:


sraab928 posted 05-30-2008 06:12 AM ET (US)     Profile for sraab928  Send Email to sraab928     
My 2006 Hummer HS SUV has the proper wiring. Using a 7-to-5 adapter disables the brakes when backing my trailer for my Grady. For my Whaler trailer I am considering using a 7-pin connector to run wires to my trailer and taking the power feed for my electric winch so I don't need to run wires to the truck all the time.
Paul_H_L11 posted 05-31-2008 01:10 AM ET (US)     Profile for Paul_H_L11  Send Email to Paul_H_L11     
I am not sure if I understand correctly, but your trailer wiring for your Hummer probably wasn't designed to take the extreme load a winch would draw.
jimh posted 05-31-2008 08:08 AM ET (US)     Profile for jimh  Send Email to jimh     
The battery lead to the trailer connector is fused, typically at 30-amperes. The fuse will decide if the load of a winch is too great.
DeeVee posted 06-01-2008 01:44 AM ET (US)     Profile for DeeVee  Send Email to DeeVee     
Jim--My 2001 Ford F-350 RV plug does actuate the solenoid to disable the hydraulic brake pressure while in reverse.

I wired my electric winch directly to the starboard truck battery utilizing the circuit breakers that were supplied with the winch as circuit protection. The plug for the winch is mounted in the location that the flat blade trailer plug resides from the factory (that plug and wiring is looped up over the wiring of the main plug in case I ever need a flat blade connection).


jimh posted 06-01-2008 08:56 AM ET (US)     Profile for jimh  Send Email to jimh     
From the sample results so far it appears that FORD and GM generally have their 7-pin RV trailer connector wired with the back-up lamp circuit to the center pin (Pin-7).
Nauti Tauk posted 06-01-2008 07:53 PM ET (US)     Profile for Nauti Tauk  Send Email to Nauti Tauk     
Just an interesting note on 7 pin trailer plugs. The 12-volt-DC that is present makes a dandy trolling battery charging circuit. Rigged with a couple of quick connect plugs and backfed through the trolling motor plug you can charge the [boat's trolling motor] battery while driving. This will only work for 12-volt trolling motor installations. Travel trailers use this circuit to charge their batteries.
Jefecinco posted 06-02-2008 08:43 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
2004 Nissan Titan also connects as GM and Ford.


Tom Hemphill posted 06-02-2008 04:53 PM ET (US)     Profile for Tom Hemphill    
My 2006 Toyota Tacoma pickup truck with a factory tow package has an RV-style trailer connection which is wired with the backup light using the center conductor. The cover for the receptacle conveniently illustrates the pin-outs:

Photo: Trailer connector

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