Well, to bypass the tweeters and Bose factory amps with my Bose system, I did this:
Sorry for the sideways picture. But anyway, I cut the wires that corresponded to the door speaker wires and soldered them directly to the provided quick disconnects for hook up to the speakers. Problem is I have no idea how your 03's factory system is set up, so maybe some pictures of the inside of the door panels would help us figure this out, if you could provide them.