Another OT trailer brake question....kinda long

Now I have a '98 Chev 3500. I kept the digital controller when I sold the Dodge. I went to the trailer parts supply store and told them I wanted a plug-in wiring harness for my '98 Chev. He sold me one, but I couldn't find a place to plug it in anywhere. I did some searching on the internet and found a FAQs page on etrailer.com. It listed part numbers for harnesses for Chevy trucks. The harness I was sold is supposed to fit '99 to '02 Chevy trucks. No harness is listed on etrailer.com for my '98.

So I went ahead and wired my controller to the same wires the old controller was connected to (the Chevy came with a controller, but I wanted to keep my digital one).

Now to my problem: with the digital controller in the Dodge, I would get trailer braking if I used the controller by hand or if I touched the brake pedal. Also, the brake lights would come on if I applied the brakes by hand at the controller or if I pushed on the brake pedal.

With my current setup on the Chevy, I only get trailer braking if I manually activate the controller, not if I touch the brake pedal. This means if I want to brake both the trailer and the truck, I have to be using my left foot and my right hand simultaneously. Also, the brake lights come on only if I use the foot pedal on the truck, not if I use the controller by hand.

Can anyone tell me if there is a plug-in harness available for the '98 and earlier GM trucks? Or can anyone tell me where I need to tie in my wiring to get full function like I had before?

Thanks for reading my long sad tale. I hope someone can help. I lost the email address of the expert who helped me when I was installing the controller on the Dodge.

I don't know what NAT stands for, but I checked it with the test light, it lit up when I pressed the brake pedal. So I found a terminal connector that slid right on that stud and put that on the end of the red wire. Bingo! Everything works as advertised now. All my other wires were already connected where they should be. Whoever first installed the other controller had the red wire spliced into some yellow wire coming out of a harness of wires that was at least 2" in diameter. The two previous owners of this truck both pulled 5th wheel travel trailers. I wonder if they've been fighting brake function the whole time?

I had the problem fixed in about 30 minutes, but then I spent another hour tidying up, putting all wires into some black plastic loom. Even though it can't be seen, I just feel better when I know all the wires look like they're going where they should, instead of running every which direction. I'm kind of anal that way.