This is for my friend;
He bought a JVC deck and has bose stock speakers(I dunno what the deck was, but it was pretty big, think it was bose also), I was helping install the deck, we had to solder a converter so the plug would fit into the deck(Provided by the audio shop we bought the deck from) we soldered it all correctly and we got it in but could get any sound out of the speakers.
He took it to best buy(Have no idea fing why, he didn't buy it there) and they said you have to rewire the bose system because it's wired differently then the rest and it they would do it for a couple hundred. I don't have a whole lot of experience so I dunno if it's true ?
Also his deck doesn't have any RCA(I told him to go with a different deck but he insisted on this one) what can he buy to add amps to the system? Would this fix the problem taking this route?