2003 Jetta, need help with stereo
 

Hello, i an the owner of a 2003 Jetta. i am trying to install an old amp and sub that i had laying around. i took the dash apart and pulled the section out that houses the radio, HVAC controls, and the cup holder. i am going to splice in some speaker wire to the rear speaker wires for the amp and i have verified which wires i need for that but for the life of me i can not figure out what wire is the one i need for the "remote" wire for the amp. i have checked all the wires on the power side of the harness and i have a couple that have +12Vdc, and +4Vdc, and the ground. none of these wires however shut off when i turn the radio off or turn the ignition off and take the key out. i also found the one fuse that will shut the radio off when pulled but it has a constant +12Vdc on it as well. i have no idea what to do. this is the first vehicle that i haveinstalled a radio in that was not GM, Chrysler, or Ford. Can anyone help me?