Re: Hooking up subs
Before we go further I'll just explain a little something champ; RCA (or low-level) plugs are not usually found on most factory head units. Rather, most head units have speaker (or high level) wires coming out.
You can get high-to-low level adapters (and in this case is exactly what your brother will have to do). This takes the speaker wires from the facotry head unit and converts their signal into RCA cables that the amplifier will understand. :)
Decent quality ones cost about $80-$100 (brands like Alpine etc). :D
Hope thaty helps. :D