I'm also lucky that my neighbor happened to have access to a high-end oscilloscope that reads both GMLAN and LIN networks - A key part of deciphering the messages that need to be captured and programmed into the microcontroller. We were able to capture the message sequences for each standalone controller, the messages from each seat, and the handful of messages that needed to be replicated from the HVAC unit. At this stage, we have this working. There is a glitch that we are trying to figure out where the seats get out of sync with the switches sometimes for an unknow reason. It's easy to reset by turning the key off and back on again. But not so easy if you are driving.
As a backup if needed, I will hide a relay and switch that cuts power (same as turning the ignition off) to the seats to reset them while driving if we can't get the software glitch figured out. But my neighbor is a perfectionist and said he wanted some time to look into it.
Here are a few pics of the equipment, microcontroller, and the start of the process of "de-wring" ~ 70% of the wires from the harness that I won't need. The pic below is just the wires that I've de-pinned from the Airbag module and were later removed from the harness.
I've been waiting for the seat programming to be done so that I didn't disrupt some wiring inadvertently while removing wires. I'm confident that I can start that process now.
Next, I need to determine where all the wiring will layout so that I can cut the hole in the firewall, mount a few ECUs under the dash etc. It's all related to finishing the cab, so I want to get it going.
Thanks, and that's all for now.