s1795so2 
i dont have access to the factory schematics for anything but my 97, but i looked that one up, and it makes sense to me. -- the RAP is handled completly through the bcm, there is not a RAP feed to the head unit at all --the RAP module tells the bcm to cut power on the switched 12v to the accessories, so there are no extra wires at the hu. (i thought it was this way until the Class II data showed up in the 04's but i dont know about the 02/03's (dont all of the radios between 97-03 interchange? ))
on edit:
I did soome more digging, and here's what I verified. (thought was the case, but found info) 97-03 didnt have class II data bus. RAP power was controlled at the bcm/RAP module that cut power to the switched acc leads. (just like taking out key)
the 04 and up have the class II data that takes place of the switched 12v lead (and controls the RAP)-- when you add an aftermarket hu, you dont get the RAP signal here without the special plug and play adapter that provides the 12v switched + RAP. --- the biggest clue in that the RAP might not work as expected is if you end up running a 12v switched lead to the new aftermarket stereo.
obviously, s1795so2, you've likely installed more stuff than I, so i havent seen every possible scenario, but it seems that's how it's supposed to work (maybe the RAP module in the 97- 03's go bad??)
