Hookin Amp To A GMC Truck

The line output converter may be two channel or four channel.  You can tell by looking to see how many RCA's it has on it.  One for each channel.  I don't know what brand you bought, but Schosche used to make one that Wal-Mart sold and all of it's speaker input wires were labeled.  You have to connect them to speaker output wires either off of the factory stereo, or close to the speakers themselves(these are usually the easiest access points to these wires).  If the amp is only a 2-channel amp, then you only need to use two sets(4 wires in all) of the speaker input wires.  If it's 4-channel, then you have to use all four sets(8 wires in all).  You should be able to find a factory wiring color code on this site for your vehicle, but I do not know about the Bose system specifically.  Also that line converter may have adjustable gain settings.  They may be recessed in the top of the line out converter itself.  You can adjust these with a screwdriver, usually phillips #2 size.  You do this if the output to the amp ends up being too loud even at a low volume. 

That's all I can say without seeing the unit and your vehicle in person, which I doubt is possible.  Sorry.