Trailer Lighting 7-pole Connector

Electrical and electronic topics for small boats
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Trailer Lighting 7-pole Connector

Postby jimh » Fri Sep 07, 2018 10:04 am

Recently I bought a new tow vehicle that came with a factory installed 7-pole trailer electrical connector. For more than 10-years my boat trailer has been wired with a 7-pole connector, and my other tow vehicle, a 1995 GMC Suburban, also has a 7-pole connector.

In the case of my own trailer and the Suburban, the 7-pole connectors were not OEM equipment. I installed them myself. To get the proper wiring of the connectors, I did some research, using on-line sources, and for the details of the GMC vehicle wiring, the enormous five volume shop manual and extraordinarily detailed schematic diagrams, drawn with their own unique style and nomenclature.

I had deduced what I thought was a correct and standard configuration for the trailer and the truck, and, since both were wired by me according to that configuration, when my trailer was plugged into my truck, every circuit worked properly.

When I got the second truck with its OEM trailer connector already installed, I hesitated to just boldly connect my trailer connector to the new truck without first performing some checks and verifying my 10-year-old self-installed wiring was compatible with the OEM connector on the new truck.

For reference I used my own article on trailer wiring: ... iring.html

I then verified the connector wiring on my GMC Suburban by using a Fluke DMM, and checked for the presence of the proper voltages on the proper pins. I confirmed that those many years ago I had wired the truck as I described in my article.

Next I needed to investigate how the new truck’s OEM connector was wired. I sat down behind the rear bumper with my DMM and a sketch from my article’s wiring diagram of the connector, and I was about to start testing. Then I saw the flip-up cover of the connector was embossed with a wiring diagram.

Fig. 1. The truck manufacturer (Jeep) had very nicely provided a pictorial diagram of the wiring it used for the 7-pole trailer connector cover.
jeepTrailerSocketCoverDiagram.jpg (23.2 KiB) Viewed 12 times

The inclusion by the truck manufacturer of a schematic diagram of the truck’s trailer connector was a great help. I quickly verified the wiring and reconciled it against my trailer wiring: the two were a match.

Fig. 2. To work out the wiring and compare the two connectors, I needed some early morning sunlight and some good coffee.
calculations.jpg (67.01 KiB) Viewed 10 times

At this point I was confident that my trailer could be connected to the new truck, and all circuits would work. The point of all this pre-testing was to avoid having a fuse in the truck blow—or something even worse happen—if my trailer (and my other truck) turned out to be (mutually) wired incorrectly for all these years.

After about an hour of time spent testing and checking, I finally connected my trailer 7-pole plug to the new truck’s OEM 7-pole receptacle: all circuits worked properly and no fuses blew.

This confirmed several elements:

—the research I had done more than 10-years ago and the article I had written then provided guidance that was accurate;

—the wiring I had done more than 10-years ago to the trailer and to the GMC Suburban was done according to my article; and,

—the truck manufacturer (Jeep) was using the same standard for the connector wiring as I had found in my research.

ASIDE: about a year after I wrote the article on trailer connector wiring which contained details about the wire colors used by GMC in their chassis pre-wired trailer connector harness (which, by the way, uses insulation color coding that is quite different from the color-coding used in most trailer or RV wiring) a colleague at my work came over to see me one day. He said he had been trying to install a 7-pole trailer connector on his GMC Suburban of about the same production epoch as my 1995, and he had searched in internet for advice. He told me my article was among the top search results, and the only one to have the GMC wire color codes. He was surprised that the author of that article was a guy down the hall at work.