Use to be four bucks including postage to buy a shop manual, now figure on at least $200.00, but a ton more of common sense safety information than actual useful information. Could try alldata.com, looking for a component placement line drawing. Practically all new manuals today require an additional electrical service manual, won't find that in the once shop manual. One trick I have used on older vehicles with all four door panels removed, was to disable the actuators, and follow the click sound of that relay. Can't find that with the noise of the actuators.
From Jim's supplied circuit, you are looking for the multiplex control unit, whatever in the hell that is. But as you can see for the three passenger doors, two relays are used to reverse the polarity to the actuator motors. If you just add even more relays with disabling those existing relay contacts, your additional relays will fry the system as you are applying both positive and a negative voltage to the same actuator terminal.
Installing remote entry is NOT an easy job.
Actually with board protocol, should have continued on with your same post.