Is it doable? I keep searching around and no one seems to be doing what I want, or I'm just not finding it. When I bought the car it had a lot of A/V stuff that was in it, including replacement speakers which were hardwired using new wire. So to begin, there was no amplifier or (I think) CD changer in the center console when I got the car, just the two plugs shown below.

What I really want, is to use a harness adapter to plug the aftermarket head unit into the stock wiring harness, and attach the speakers to the stock connections, so I don't have to run any additional wiring. The top plug in the picture has continuity to the wiring plugs for the speakers in the doors, and I've seen people referencing just jumping/cutting the speaker in/out lines that were going to the amplifier. Is it safe to assume then, that 2 of those wires are left speakers, 2 are right speakers, and the remaining 2 are the input; so I could just jumper them together?

Also quick unrelated question: I found an overhead console with a homelink garage door opener in it, from a 98 Blazer; is there any reason it wouldn't work on my 02 Blazer (which did not come with a homelink system)?

 

I'm assuming then that the HU the previous owner had installed in the truck was taken out before you bought it or they had a separate amp for the speakers?

Is the additional wiring they installed going to that smaller plug you have there?

It's hard to say with a great amount of certainty exactly what direction to go because without getting in the truck to see exactly what and how they did the last setup there's no way to tell you exactly how to do what you're wanting to do. If I remember correctly the factory Bose system had it's own amps and to use the factory wiring with aftermarket equipment those have to be bypassed or custom wiring has to be done to connect the aftermarket HU's pre-outs to the Bose amp inputs.

It sounds to me like they ran all their own wiring to the speakers to bypass all that problem. If the additional wiring they added already exists why not use it? You could get a standard harness adapter to get the switched 12v, battery constant 12v and ground from the factory harness and just wire the speaker outputs up to their wiring separately, it doesn't have to hook up to the factory wires.

Either way its going to take a bit more detail on all the particulars to do much more to really help without being there to look at it.