Factory wire diagram to help install aftermarket amp and subs in 2004 GMC Sierra crew cab w/ bose

if youre gonna keep the factory radio in then you need a line out converter.   since you have the bose system, you have to tap speaker wires after the amp.  the hard part for you is gonna be finding the amp!  im not sure where it is on your vehicle.  check under the console.  pull the whole thing up, i have seen alot of newer model GMC bose amps there.  if not there, a few other good places to check are under all the seats front and back and behind the glovebox.   once you find the amp.   tap the rear speaker wires for the LOC.  they are:

Rear left +  brown

Rear left -   yellow

Rear right + dark blue

Rear right - light blue

hi there just go to the panels were the rear speakers are and remove tip tap the cables

Rear left +  brown

Rear left -   yellow

Rear right + dark blue

Rear right - light blue

get a high to low converter and tip tap  it to those cables and that is it you will get the rca for tou amp

You wont have any luck tapping into the speaker wires at the speakers. Bose put filters on its amp and only sends higher frequencies to the speakers.  Your amp is located inside the console between the front seat. If you just want to add a sub I have sucessfully tied them into the existing sub. It is a dual coil unit mounted just ahead of the amp in the console. Find the two twisted pairs that go to the factory sub and tie into them. I can't remember the colors but they will be the only twisted pairs that leave the amp headed tword the front of the truck by themselves. You will get a great signal (high level)for your sub amp since they are already passed through a filter. You also retain the factory level controls. You will have to play with phasing a s again I can't remember the correct combo. Next time I do one of these I will write down the colors.

Just as a side note make sure to unplug the amp while you are working on it as they are powered all the time. You don't want to toast it.

Got an LOC and I know where the amp and harness are ( previously installed to another factory radio ), any help with a signal wire off the amp harness