Easy one - 4-wire trailer wiring harness question?

[AJMBLAZER]

I'm doing some clean up work on my trailer and vehicles and would like to install the trailer wiring harness I bought for Big Ugly about 3 months ago.

It's one of those "unplug the factory harness, plug this in, then plug the factory stuff into each side of it" setups. Supposed to just fit into the factory wires without any splicing or anything permanent.

The connection part looks like four circular tubes arranged in a 2x2 square:

OO
OO

Now here's my question...anybody know on a 1986 K30 where this connection would be? I can't seem to find anything obvious and before I start pulling on 21 year old wires I figure I'll ask you guys.
Anybody know if a CUCV pickup's additional wiring would complicate this?

 

[Muddytazz]

should be on the drivers side of the rig, inside the frame rail just under the body

 

[77crewcab]

Mine is located up behind the bumper just to the driver side of my hitch.

 

[Blue85]

Yes, what they said. You are actually tapping into the wiring harness for the taillights. The two halves of the connector will look just like the ones on that adapter plug you have. That series of connectors is called "weather-pack".

 

[AJMBLAZER]

I looked again today and didn't find anything like my four circles. However I did find hinding on top of the d-side bumper mount the object in the picture below.

Did GM sneak in some older parts on me?

 

[Jason4x4]

that is the one you need, you probably have the wrong adapter.

 

[AJMBLAZER]

From talking with some of the CUCV owners over on SteelSoldiers it sounds like this is another one of those places where GM built the CUCV's with old stock. Instead of updating this stuff to the newer design in '85 they just kept using the old stuff on the CUCV's to get rid of it.

NAPA says I can switch it if the thing looks serviceable. Been out of the box once. Hopefully I can swap it for the correct one tomorrow.

 

[dyeager535]

As someone mentioned on the other post, it likely wasn't GM being cheap, it makes sense logistically and tactically to have complete parts interchangeability, (multiple parts manuals? Not being able to just order an adapter and get the right piece? Etc.) and not changing things saved GM the money of re-design. And of course I'm sure it was an easy way to dump old stock.

Sucks that they did that for you though, I can't stand those connectors.

 

[AJMBLAZER]

Yeah, I figured as much after thinking about it. I worked on gear in the Marines that was 40 years old and had been revised half a zillion times...probably good thinking on GM and the military's part to keep as much of the CUCV's unchanged as possible.


So...got the new plug all hooked up...but there's an issue. The lights work correctly on the pickup - flashers, turn signals, running lights, and brake lights and ditto for the trailer when I hook it up to the wife's XL7.
Hook the trailer up to Big Ugly and the running lights work fine on both sides of the trailer as does the flasher/signal and brake light on the driver's side of the trailer. However no flasher/signal or brake light on the passenger side. Nothing changes on the truck with the trailer connected.

I did notice that the male end of that plug in my picture above is missing a..."digit" . It's only got 3 of the little prongs...yet how come my lights work fine on the truck?