Not really an upgrade as much as a pretty up. After looking at the raggedy looking platform hitch glaring out from under the bent rear bumper since it's arrival I took it upon myself to do something about it. So down came the unit and then it was a total strip and cleanup. Then a repaint with some durable black epoxy.
Boy! Did that ever make a difference! Once it dried I reinstalled the unit. I even managed to locate the factory angled mount bracket for the 7-pin plug. That was installed after a clean up and repaint. As a nice addition I located an after-market multi-tow pigtail replacement that is a direct plug-in replacement that includes a 4-pin with the 7-pin round. No more adapters needed.
After locating a good used insert, pin and hitch ball they too were refinished and assembled. A trim plug for the hitch tube when not towing finished it off nicely. Some grease in the hitch tube and on the insert will keep it usable. I hate it when people are too lazy to take the hitch extension out. It looks goofy! And they are a bear to get out once they are in for a while! It now looks very nice under the new bumper.
Once the hitch was down it wasn't long before it was discovered that the rear segment of the factory tow harness wiring was in poor shape. Once more a run through the service revealed that the rear segment was pluggable mid-frame. So rather than trying to repair the extensive damage I salvaged a nice harness at Parts Galore. And that same trip I found a serviceable brake control module for under the dash. With those in hand it was back to the shop.
Replacing the rear tow harness is a simple task. Unplugging the mid-frame connection and plugging the new harness in. Then it's a clip for clip run. The cool part of the factory GM 7-pin is that it is pluggable at both ends, The trailer connector head simply plugs to the end of the cable and keyholes into the retainer bracket, And for good measure I just got a new one. It all went in nicely.
So I moved my attention to the front under-dash for the brake controller. This van apparently had a controller at one time because a mount bracket and some hacked wires were at that location. Unfortunately the previous owner had done some creative wiring to get it to work. Back to the books.
The revelation was that the primary fuse panel in the front bay has two 30 amp fused external lugs specifically for the two harness power leads. [ BRAKE feed / AUX feed ]. But oddly there was no cabling to them. So I fabbed a short 2-wire primary feed harness and fed it through to the under-dash area. After some simple hook-up to the controller and rear harness feed a quick functional check verified that all the power was where it belonged to do the job.
So I now have a full electric brake capability and when I don't need it, which is most of the time, all I do is pull the two fuses and it waits until needed.
Found the block heater: While I was exploring and fishing the new harness through to the dash I discovered what appeared to be a 3-prong extension cord end wrapped around the brake lines. It turned out to be the plug for the factory installed block heater! Common on up-north diesels.
This is more of general info on a 7 pin wiring hook up. What goes where. The whole point behind this segment is for the checkout of a 7-pin trailer hookup. And the critical part is the fact that in a 7-pin hookup there are some feeds not found on a 4-pin hookup. The primary element is the feed for the electric brakes, be they surge or solenoid. The other pair are a full 12-volt feed and an aux feed. But the main consideration is the electric brake feed.
The cool thing is a great update out there that incorporates the 7-pin round socket with a traditional 4-pin socket all on the same bracket. This is called a multi-tow feature and most of the newer vehicles come with thse factory installed. But they make the pieces to update the older single socket units with a simple pigtail.