01 expedition with premium sound

i recently installed an amp on my friends 01 expo, the amp did not work properly since the right radio was not around(no sub control), after installing proper radio, i couldnt get the amp to sound properly unless it was adjusted to either the left or the right on the fader. does anyone know how i can dissable the factory amp and where its located? i know the best way around this is to just run new speaker wires to the front, but friend is too cheap to purchase speaker wire yet alone some good speaker wire.