Thread: adding an aftermarket radio to bose/onstar/monsoon in 97-03 & 04-08 [*]

Originally Posted by s1795so2

I am thinking that this is the case: It seems like it does depend on options, and I think toasty and archemedes figured it out. Rap may be retained (sometimes) and if it is the h/u does not stay on, just the accesories. Which most people don't even know or care that the lights are on the rap system too, they just automatically think of radio.


Wow finally a forum that has good debate and convo in the audio section! I think this is a good sign for me, haha.

i think we've about got it down, but if you'll excuse me, i'll ramble on a bit :P


from what i can see, and from the stuff i've done with my other vehicles (in my 97, and i hypothesize thru 03, since they use the same radio) the RAP function is completely separate and on it's own, not tied into the audio system directly, however the RAP does cut power to the HU when it does everything else. there isnt any exra harness to retain RAP on these because it is 'upstream' if you will. so unless there is something broken with the RAP circuit, any aftermarket stereo in these cars SHOULD operate like the factory one with the RAP functionality.
(note that the radio in these years did NOT control the chime functionality, and 19990-2003 had onstar capability, but were not Class II data linked, so no RAP issue here either.)

now in 04, everything is different. The Head unit and onstar, and other items, including RAP are controlled through the Class II data bus. (easiest way to note this on any GM vehicle is if it has RDS, then it's on the Class II data bus (or higher, like the new GMLAN/CAN bus... but we'll not get into that) (and they communicate with each other this way) there is no switched 12v lead at the radio. the BCM sends a signal over the data bus to turn off the radio at the RAP time out. The head unit also plays the chimes thru the factory speakers. If you remove the stock head unit, and wire it up directly, you have to add a 12v switched lead-- if you add it from a RAP source, then that's OK, but if you run it from a circuit that is not, then you loose RAP on the head unit. you also loose Onstar because the onstar unit cannot communicate over the class II data line to the aftermarket head unit doesnt have one. the special adapters that are avaialbe (handfull of companies make them) interperet the class II data and feed the onstar info to the head unit in standard audio format, and also gives you the 12v switched lead, controlled by the class II data, which allows you to retain RAP for the aftermarket head unit.

ok... that's enough rambling for one post