Sub'd.

 

I'm here as well, my new boat trailer is going to have EOH brakes. Hopefully I never have a problem, but I'd like to be prepared.

 

Couple of tech posts on GM Tech link. Pertain to controller installation only. Might be some info for you there: one for a 1500 and one for a MD. Both use a factory supplied harness that plugs into j box under dash that supplies power and ties into lighting circuits.
I think you could use the factory wire harness from dash to rear and trash the relay/module at the back and splice that back together.

Personally, I prefer the Hopkins plugs and receptacles but pollack works as well I hear.
When you finish post the info- lots of fellers on here have problems on ITBC's (I never have by the way)
Should make a nice mod.

As for the factory ITBC working with EOH brakes: mine works perfect on the 4500 and did on the 3500 as well. I had a Tekonsha on the Pete and it was programmable for trailer size, type of brake, and number of brakes. Worked flawlessly for 4 years on 4 different trailers.

 

Couple of tech posts on GM Tech link. Pertain to controller installation only. Might be some info for you there: one for a 1500 and one for a MD. Both use a factory supplied harness that plugs into j box under dash that supplies power and ties into lighting circuits.
I think you could use the factory wire harness from dash to rear and trash the relay/module at the back and splice that back together.

Personally, I prefer the Hopkins plugs and receptacles but pollack works as well I hear.
When you finish post the info- lots of fellers on here have problems on ITBC's (I never have by the way)
Should make a nice mod.

As for the factory ITBC working with EOH brakes: mine works perfect on the 4500 and did on the 3500 as well. I had a Tekonsha on the Pete and it was programmable for trailer size, type of brake, and number of brakes. Worked flawlessly for 4 years on 4 different trailers.

Do you have the link to that Techlink post? I've never navigated that site but nothing popped up when I did a Google search.

I'd consider reusing GM's wiring but even if I wanted to it's not clear that doing so will be straightforward, or even possible. The K133 brake control module that's located above the spare tire appears to be connected to the cab with only a small signal wire; note in the diagram and picture below that the only "large" wires are ground, battery voltage in, and brake voltage out (black is not visible in my picture, but it's there, trust me...).

In this diagram you can see a reference to "W24 Blunt Cut - Trailer Brakes Provision". I'm pretty sure this refers to the 4-pin terminal on the panel under the left side of the driver-side dashboard, to which the aftermarket controller connects.

Only problem is, when I connect the controller, it doesn't see a trailer. This occurs whether the K133 module is connected or not.

But that's consistent with the fact that there are apparently no wires large enough to carry brake current coming into the K133 from the cab; instead it's just a small signal wire and it's the K133 that's actually applying the voltage (and hence current).

I even cut open the loom leading from the K133 and BCM toward the cab. I did not see a large blue brake controller wire. Instead, I saw two large red wires with green strips. I believe one of them is the power supply to the K133 and the other is the trailer receptacle 12V AUX supply.

This is about the time when I page @ChevyTech77 and @Mtu Alum and ask how they would install an aftermarket controller in this truck. More specifically, is there a wiring harness connected to the other end of the 4-pin terminal under the dash tucked away somewhere that I can tie into? Or is it a dead end because the truck has the integrated controller and I need to actually run new wire all the way from the controller to the receptacle?

 

I agree that it’s absolutely asinine that GM cuts power to the trailer brakes if there is any fault or condition that triggers a check trailer wiring message. Couple days ago I’m cruising the freeway at 70 at just under 30,000 pounds and I get the check trailer wiring message. Then I hit traffic, and have no trailer brakes. Unbelievable. I mean truly unbelievable the level of stupidity of the engineers as the OP said. Here’s the kicker, I can pull the breakaway pin and all brakes work perfectly. So I pull all the hubs, one magnet has wore through to the coil. So one magnetic is bad yet I have no brakes. This is a huge deal. So glad it happened in flat Minnesota and not in the mountains when I’m headed out west next week.

It’s frustrating when people blame GM or engineers for doing stupid things that really aren’t that stupid, but this is one situation where they really are stupid and this needs to be addressed.

 

Yep. The only time it's acceptable for the controller to self-disable is if there's truly a dead short on the trailer brake circuit. Other than that, I expect the damn brake controller to be applying voltage as it incinerates itself or melts. The kicker for me was that clearing codes resolved the "issue". Hence my interest in replacing this ridiculousness.

 

About a 100 reports to the NHTSA might get them to look at it.

 

I reported it to NHTSA.

 

Sorry JD, I should have typed GM Upfitters instead of TechLink.

They changed the site format and its a pain to navigate now but look at the bulletin lists-- just check all bulletins and weed thru them til you find the ones you want.
They pertain to aftermarket controllers. using the factory wire harness pigtail that used to come as loose equipment on new trucks prior to ITBC

 

Sorry JD but I am of no help here as I have never replaced my ITBC. 😂

You saw on one of the other threads how I fixed the EOH brakes for my camper via the adapter install......

 

Making progress. I figured out that the brake voltage output wire runs from the X61A junction block (under the dashboard, left side of driver's footwell) to pin 32 on the X138 receptacle by the under-hood fuse panel. I've highlighted the pin in yellow on the receptacle side.

And here it is on the wiring harness side; this is the side that runs back along the frame rail. Notice that there is no conductive lead associated with pin 32; it's vacant.

According to this document, I need a wiring lead with part number 13327155 to insert into the wiring harness, and then I can run my brake control wire from that lead back along the frame to the receptacle. But a Google search for that part number gives me nothing. Any ideas where I can pick one of these up?

Next step is to splice into the receptacle wiring, but I'm going to do it without cutting any of the OEM stuff. I ordered the following two parts to make an a "plug in splice" connection:

What I'll do is cut the receptacle off the 35508 and connect all of the plug-side wires to the wires from the 40985 with the exception of the brake control wire, which will come from the new wiring harness lead once I acquire it. Then I'll simply connect it in-line with the harness that comes off the truck and plugs into the back side of the 7-way receptacle; in the pic below I show the truck-side and receptacle-side on the left and right, respectively. By doing so we bypass the ITBC completely.

I am considering running a new/dedicated ground and 12V aux conductor while I'm at it, though. In that case I would tie those new conductors into the inline splice rather than reuse the OEM conductors (actually, I might just combine the OEM ground and 12V aux with the new conductors to further reduce voltage drop). Although I think at first I will just run the brake conductor and use wire loom large enough that I can easily ram another two wires in there if I decide to run new ground/aux wires in the future.

 

Just saw this one JD. Really, I haven't been ignoring you. I've been on vacation for a week and a half and darn near off grid.

I had the dreaded "Check Trailer Wiring" message on the 2012 every few seconds for hours at times in the past. Everything would be fine, then run into some rain and start getting the never ending annoying message. But everything was still working fine and no fuses blowing. So, WTH?

My biggest problem typically seemed to be where the trailer pigtail plugged into the truck receptacle. I'm about as much of a 7-pin round RV plug fan as I am an ITBC fan. It's the worst trailer plug going. Easy to plug in and unplug though

I just put up with my controller in the 2012 but if I had undertaken the project to replace it, which I had definitely considered, I would have ran a totally separate system from the fuse box to the back bumper. I've never had problems with Tekonsha, Kelsey Hayes or some other no name brake controllers....never.

Looks like you're getting it figured out. Keep us posted.

 

Well the short version is, it's working. I'll post a DIY thread later with all the details.

 

I have tried several different high end aftermarket controllers on my 03 2500 Duramax. I hate all of them. My 2020 1500 gasser has the fancy trailer package on it. I absolutely love the factory brake controller. And the TPMS for the trailer. I have all 4 of my trailers set up in the app and it's plug and play. Just select the trailer in the app and everything works. I still use the old Duramax for long trips with the RV due to better fuel mileage and larger fuel capacity. But the 6.2 pulls fine and I use it for most short trips. It's nice having TPMS on the trailer. But there is no aftermarket controller that works as smoothly as the factory one. It matches the trucks brakes perfectly.

Sent from my SM-T510 using Tapatalk

 

I have tried several different high end aftermarket controllers on my 03 2500 Duramax. I hate all of them. My 2020 1500 gasser has the fancy trailer package on it. I absolutely love the factory brake controller. And the TPMS for the trailer. I have all 4 of my trailers set up in the app and it's plug and play. Just select the trailer in the app and everything works. I still use the old Duramax for long trips with the RV due to better fuel mileage and larger fuel capacity. But the 6.2 pulls fine and I use it for most short trips. It's nice having TPMS on the trailer. But there is no aftermarket controller that works as smoothly as the factory one. It matches the trucks brakes perfectly.

Sent from my SM-T510 using Tapatalk

It's all good 'til the BCM throws a DTC because some resistance value is 0.01 ohms outside of the "acceptable" range and disables your ITBC completely (but at least it kindly recommends that you SERVICE TRAILER BRAKE SYSTEM) as you're descending a hill at 70 MPH with a 20,000 lb trailer.

There's no app that'll save you from that.

 

Couldn't agree more. The integrated controller is spectacular when it's working, so you love it. When it's giving trouble, you hate it. And while I also completely agree that it's tough to find an aftermarket controller that functions as nicely as the integrated unit, at least the A/M's work and don't drive you crazy with the same message over and over every few seconds, then leave you without brakes when you need them most.

The 2004 F-550 that I just put on the road last year had what looks like an old, cheap Reese controller in it when I bought the truck. I pulled a flatbed trailer with it Saturday that has electric over hydraulic brakes and that crappy looking old controller even worked on it.

Nice job on the install JD. I knew you'd get it done.

 

Couldn't agree more. The integrated controller is spectacular when it's working, so you love it. When it's giving trouble, you hate it. And while I also completely agree that it's tough to find an aftermarket controller that functions as nicely as the integrated unit, at least the A/M's work and don't drive you crazy with the same message over and over every few seconds, then leave you without brakes when you need them most.

The 2004 F-550 that I just put on the road last year had what looks like an old, cheap Reese controller in it when I bought the truck. I pulled a flatbed trailer with it Saturday that has electric over hydraulic brakes and that crappy looking old controller even worked on it.

Nice job on the install JD. I knew you'd get it done.

Thanks. The only part that wasn't straightforward was inserting a new terminal into the X138 chassis wiring harness (the socket for this terminal is vacant in trucks that have an ITBC). I was able to hack it with some terminals I got on Amazon but it's not pretty:

And here's how the harness looks reinstalled. The holes in the plug were too big for 10 AWG so I had to use a short length of 12 AWG which I then connected to the main 10 AWG wire.

I have ordered what I believe are the actual OEM terminals for that wiring harness; once I have them I'll replace my mangled terminal with the correct one and post a more thorough DIY. Alternatively, you could cut off the wire leading to pin 32 in the block to which the harness connects and splice into it directly, or just run a new brake wire through the firewall from the controller (the other three conductors the brake controller needs are supplied in the junction block that you plug into under the dashboard).

The only other questionable part is how to connect the new brake wires into the existing 7-way if you're reusing it (like I did; I calmed down after my initial bit of rage thanks to @sambor's recommendation). I did it basically the way I describe above by creating an inline splice connector by cannibalizing some Hopkins brake controller hardware and some MC4 solar panel connectors (which are awesome because they're completely waterproof at both the wire-connector and connector-connector interfaces). This less-than-pretty contraption simply goes in between the existing truck- and receptacle-side connections at the bumper, up above the spare tire:

You can see I doubled up the existing ground with the new one I ran from the battery; here it is taped up and ready for installation:

And here it is added to the rat's nest of crap behind the bumper, all hooked up:

The big thing here is that there is no existing wiring to "reuse" between the wiring harness under the hood and the receptacle because the ITBC's user interface in the cab (analogous to the buttons on an aftermarket brake controller) is physically separate from the controller itself above the spare tire (where the brake voltage is actually applied), and the only connections between them are small signal wires incapable of carrying electric brake current. So you'll have to run new wire but you can leave the ITBC module above the BCM connected and simply install this splice connector to use the aftermarket controller, and if you wanted to revert the modification or use the ITBC for some reason you'd just lower the spare and remove the splice connector and reconnect the plugs as they were from the factory.