I have a 99 SLT With the infinity sound .I tried to hook up after market speakers in the rear doors. They were brand new and they wouldnt work as they should . If i hook up an aftermarket cd player do i have to run all new speaker wire and can i just plug it in
with the adapter you can get?
also how do i bypass the built in amp?

 

If you find the amp( passenger side kick panel) it will have two wiring harnesses. Unplug the harnesses and cut the wires. use a little 9V battery to isolate each speaker( the speaker will pop, when you connect the circuit with the battery). Mark each of the four speakers, and run your speaker wire from the head unit to where the amp is. I did this a few months ago and replaced HU and 4 speakers in under an hour. i suppose you could cut the other harness coming out of the amp, and splice the wires together so you dont have to run new speaker wire, but i didnt feel like messing wiht it. GOOD LUCK