i have a 1996 grand cherokee. i installed a aftermarket cd player. everything works, but no sound. i used a wiring harness ease installation. on the factory radio there are 3 connectors but i only used 2 for my cd player. the other connector is 2 wire connector. when i plug in the factory radio without the 2 wire connector i get sound. not sure if there is an amp i need to hook up or if it is my cd player but i just used the cd players 2 weeks ago.... any ideas??

 

if you will use you headunit to power your speakers you need to bypass your infinity amplifier at back under your back seat. to do, you need to find corresponding wires going to doors. my pioneer headunit is working like this way.
if you want to use factory amp, you need to trigger it, so to do this, you will connect green/red wire (from black socket) to amplifier remote wire (blue)on new unit.