new hu, amp in 2003 gmc with bose

Hi guys & gals, I just bought a 2003 GMC truck that had the factory Bose sound system in it. The factory (Delco?) head unit had already been pulled and a Clarion VRX585USB had been installed by the previous owner. There is also Probox with subs and an amp installed under the rear seat. I'm not getting any warning chimes and the OnStar audio isn't coming through. I also noticed that none of the front speakers are working so I pulled the dash trim to see how things were connected. I know that there is an Axxess GMOS 4 adapter installed in between the factory harness and the Clarion power harness however, there is nothing installed on the factory speaker harness so that would explain why nothing is coming through the factory speakers.

Sorry, but for some reason the post posted before I was finished...so continuing on: I have searched the forum enough to know that in order for the chimes and OnStar to work, I need an adapter and I thought that the Axxess that is already installed should work, but I think they forgot to put in the harness that controls the Bose amp. The output from the Clarion head unit is only going out to the amp then into the Probox so there is nothing going into the factory speakers via the Bose amp (I am assuming that it is still there). Here is what I think I need to do, but please correct me or give me a better solution if you have one. I am going to replace the Clarion VRX585USB with a Clarion VRX785BT that came out of my old vehicle. I will then replace the Axxess with a PAC OS-2BOSE radio adapter in order to have the chimes and OnStar work through the factory speakers. I also want to install A PAC SWI-Jack so the steering wheel controls will work. What I'm not sure of is how to combine the factory system and the after market amp/sub. Right now the front (L&R) and rear(L&R) outputs of the Clarion are wired directly to the amp and Probox. What I think I should be able to do is hook the front and rear outputs of the Clarion to the PAC adapter then into the factory harness to control the Bose amp and speakers. The Clarion has one(L&R) non-fading output so I'm thinking that should handle the amp and subs but do I need to put splitters on the non-fade output to duplicate the front and rear lines that are currently connected? Sorry for being so long-winded. I hope that is clear enough for some of you experts to chime in and give me a few pointers. Thank you! Tank

Surely someone has some knowledge of this system......

I'm guessing the amp is a 4channel? First thing you should do is follow the output speaker wires from the amp and see if they are just connected to the subs. If they are save yourself some money and use the GMOS-4 that you already have in there. The SWI-JACK will be cake to install too. As far as the non-fader, if there are 2 sets of rcas going to the amp, I would imagine there are 2 4ohm subs bridged mono 1 on each set of channels on the amp. if thats the case, Y them together from the non-fader output.