The "tow" button isn't just for towing. It also has applications for carrying weight, as the 3500 will carry some serious weight. I just went through this on my '16. I just tied in to the rear lamps on each side. I didn't want to spend too much time looking for something that may not exist.

 

I saw the same connector under the van at the rear. But nothing worked for brake lights, turn lights. After doing some looking on the net for a way to get trailer lights to get hooked up, I found this.
https://www.etrailer.com/tv-install-...an-118392.aspx
You can get everything from etrailer. Yes you have to do the work. If your van is in the picture, you are going to have plastic covering up everything in the back. It was not that hard for me to get it off. Make sure you get the right connection before you put it back together. Also you will have to put the green wire for the right over the top.
I also took and put LED lights in the rear & front. You will need LED Light Load Resistor Kit - LED Turn Signal Hyper Flash & Warning Fix for each light. I got mine from https://www.superbrightleds.com/sear...tors/resistor/.
When you put LED lights in the rear, make sure you use the brightest white lights you can find. go here and you will read what I am saying. https://www.superbrightleds.com/cat/tail-brake-turn/
Here is another place to look at, Super Bright 3156 3056 3157 3057 LED Corner Signal Backup Lights Bulbs



I put another LED on the inside turn.



This is before I put the inside LED in.
Let us know what you do.

 

I had same question back in April on this forum. That plug is for the sensors. I was told the wiring could be in front of spare tire. Haven't looked.

Kenny

https://chevroletforum.com/forum/exp...le-plug-82537/

 

AlpineKid67
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Thanks for that post about the LED lights... I have tinted my lenses and that would work out great.....
I booked marked the web pages....
so to touch base more with your approach .... tell me did you go with the Yellow round version
could you post which ones you actually went with ? there are many to choose from .

 

I figured I would try to post some pics that might help your endeavor of locating the wiring that is if your van
has said wiring..
Mine has been mangled badly... the owner before me said he never pulled anything with the van it was
mainly used for work it was a contractor that laid tile.. for a living...
so I will start out my pics working from the back of the van...
My wires are faded from the elements of being exposed to the outside conditions ...but after pulling back the
wire loom the bigger wire that is still connected is RED with black stripe.

 

So after the last 2 pics I moved to the side of the van..
after the rear wheel and before the rear wheel...
look at the wire loom running along attached to the
frame.. thats said trailer wire loom on my 3500

how ever.... I dont believe all 7 wires come into the van

 

I believe that it splits off at the ABS system

 

Here are the pics of the wires coming into the van

 

https://youtu.be/UlEJWaahwpQ
T-connector for trailer lights is behind the right side tail light (Under interior panel for Non-Cargo Vans).

 

I found the wires under my dash on my 2018 Express and got excited that maybe there was wiring to the rear of the van for my brake controller, I was disappointed. I used a tone generator to trace the wires out and on my van they only go as far as the fuse box under the hood. The only way to access them is to tear apart the wire harness, not worth it. Easier to just pull new wires to that location. My van has a simular connector in the rear and it has nothing to do with trailer wiring.