Hey Sidearms, I think we can troubleshoot which pinouts on the PCB go to certain items on the supplemental boards and controls from the harness you have. Once you attach the main pinout harness to the PCB (which it should only fit one way), we'll be able to figure out which guys go to the power supply. Usually, on those harnesses, the heavily wired end is where you start. Black ground wires are usually on the end (first four maybe?), then +5V red wires( another four?), +12V orange (two wires?) and so on.
I just don't know how many people are out there who both A.) own this game or B.) own the schematics.
Do you already own a cabinet with the power supplies and transformers and such to test it on? At the very least, we should be able to hook up the wiring to your monitor, and get the main power wires hooked to the power supply. Once we see that the game is on screen and working, we can then get steering to work, then gas and brakes, shifters, and lastly, the sound boards.