05 F250 Powerstroke FX4...

Still new to the truck and trying to learn a few things. Haven't posted pics in the "new member" section because, technically, I'm not a new user - I just went a LONG time between postings. AND - I am waiting until I can clean it up before I post pics...

With that being said:

First question:
I would like to install my old sound system in the truck - which includes two amps. While this may be a dumb question, I would rather be dumb for asking than stupid for screwing something up...

Which battery do I hook the power supply wires to or does it make a difference??? I will run 4 awg wire to a power distribution block before I run it to the amps (if that matters).

Second question set:
My power rear window slider motor is not working at it's fuill potential - or barely working at all...it will open the window about 2" then stop. Some days it will open it up about 3/4 of the way open and then stop.
Is this a motor issue or is it a track issue?
Is this a common tings with these trucks?
How hard might this be to fix?

Thanks in advance