that my friend is a HI/Low converter, they use those when people want to run subs but not pay for a new deck, it basically takes rear speaker feed signal filters is for an amp (only allowing the hi's and lows thro) then converets it to rca so u can run a amp. make sence? so the rca is the output to the amp then the otherside u hook up the rear speaker from the deck to, then it should also have a output to the speakers to it goes INLINE between the deck and the rear speakers...... hopefully that makes sense...?