Alright. I've been sitting on this for quite a few years and I've just been dragging my feet too much too get it out to the public. So, I'll get on with it.
Light Duty Elecrical manual (25-3500) http://gmupfitter.com/files/media/ph...Electrical.pdf
Medium Duty Electrical manual (45-5500) http://gmupfitter.com/files/media/ph...Electrical.pdf
In the Light Duty manual navigate to section C-14 thru C-15 which are pages 72-73 of the PDF. Take note of pin 11 and 53 of the C2 connector. Notice they say unused.
In the Medium Duty manual navigate to C-21 thru C-22 which are pages 80-81 of the PDF. Take note of pin 11 and 53 of this C2 connector. This manual says:
C2 pin 11 (exhaust brake telltale)
C2 pin 53 (exhaust brake control)
This is the thing that got me to thinking 4 or 5 years ago. We all know that the '06 and '07 MD trucks that have the RPO of LLY are actually packing an LBZ engine with an MD tune of only 280hp, (or something close, or whatever) while the '05.5 - '07 classics have the same setup but have the LD tune of 360hp. So, knowing GM is all about recycling parts, programs, computers and whatever else, I wondered if they left the logic for the Turbine Brake from the MD programs in the LD programs. So, on a hope and a dream I wired up my switch according to the diagram of the '07 MD w/ RPO LLY. Wouldn't you know it actually worked. They did leave the logic for the exhaust brake in the LD ECMs. HOWEVER, the brake only activates while the TCC is locked up, eg. T/H mode activated. Also, with the exhaust brake activated it sends the TCM into a more aggressive down shifting map. Being, what I would refer to as, a power user of EFI Live I also attempted creating a .cax file to add tunability of the brake, but it turns out you need ALOT more knowledge of binary addresses and such that I don't know. I inquired a fellow from NZ who has made cax files before for gasser but he couldn't help me. I inquired with Ross too, but I never got very far with him. He is an extremely busy fellow. Enough history. Here it is. Im not going to tell you how to make a switch, and I'm not going to tell you what the part numbers are for the ECM pins. But I will tell you how it works and what you need to do to get it to work.
The way it works.
When C2 pin 53 is grounded this arms the exhaust brake. When all conditions are met the brake will activate. (vanes close to 100%) When the exhaust brake is actively braking pin 11 of C2 is activated sending 12v to a lamp if you choose. IT IS IMPORTANT to use an incandescent lamp and NOT an LED to act as the telltale. I originally used an LED as my lamp and it was causing some sort of fault with that subsystem making the brake engage and disengage rapidly, switched out to an incandescent lamp and it solved the problem.
Q. Do I have to have EFI Live to make this work?
A. Nope. This is a factory loaded feature. However, EFI guys will love being able to have 5 tunes with and without the turbine brake instead of making one tune with the brake and 4 tunes without.
Q. Will this work on my 06 LLY/ Bosch controlled LLY?
A. Yes. I have tried it on a few different OS's and an 07 classic. I haven't ever flashed the newest, so I cant say about that one.
Q. Will this work on my '04.5 to early '05 LLY?
A. Yes and no. It (the ECM) doesn't use the turbine for braking. Instead, just like the MD's for that year range use a flapper in the exhaust to act as the brake. I have tested it and it does power a pin to activate a solenoid for the flapper valve on the LD trucks. Figure it out for your self. Apply the knowledge learned here to your LLY and you'll figure it out.
Q. Does this work for LMM's?
A. UPDATE: I have gotten a few reports now of this mod working on LMM's. One truck was an '08 and the other was an '07.5. At this point I don't have any other information as to what OS is on either of those trucks so I can't say for sure what works and what doesn't.
A. I have done very little messing around with it on an LMM years ago and I cant tell you which OS I did it on, but the logic in the ECM is there but doesn’t activate the brake. It does send the TCM into the same down shifting pattern as the LBZ but nothing happens with the turbo. Again mess with it your self maybe you can figure it out.
Just for kicks here are a couple of pics to help you folks find the correct pin locations.