The majority of those set-ups Monsoon/Infinity, they are all tied into the head unit and the amplifier located somewhere in the car. If you have installed the head unit and connected the front and rear speakers to the outputs, it wont get to the speakers because of the amplifier. What you can do is when you find the amp basicaly butt connect the speaker wires, tape off the power remote and ground to the amp, and well tada the amp is now by-passed. Now they dont make it easy on yah with the speaker wires, an easy way to figure this out is to pick up a Chilton's which has the whole lay-out of it. Or if you have the time and patients take a AA battery and when you get the right + and - to the proper speaker it will make a slight pop noise in the speaker. The Chilton will also have the spot where the amp is located too. They dont make it easy on yah thats for sure. I went through the same thing with my Explorer. Its a pain in the BUTT! Good Luck