adding an amp and subs - need help!

does anyone know how to connect an amp to the OEM stereo in a focus?

There is a thing at Best-buy that you can buy, not sure the name or anything my friend told me about it, but it splices the wires into RCA connectors which should work just fine i think its like 15 dollars.

that is for an aftermarket deck
let me go get my stock deck out of my closet and and i will look at it
what year is it?

if im right you are going to have to use a speaker lvl inputs
which plugs into the green plug on the back of a stock focus deck
im not 100% sure but im thinkin that is right

okay...did the amp come with a "high level input" wiring harness that has like anywhere between 4 to 6 wires on it...you splice that into the rear speakers...that is what it is there for...my alpine came with one and so did all other amps that i bought