What Is The Red Wire For On a Car Cd Player?

The red wire on a car CD player, is a wire that provides a constant 12 volts to enable the CD player to turn on. The red wire on most car head units, connects to the yellow memory wire and then both are connected to a constant 12 volts source. The red wire should always have a in line fuse holder, with a fuse inside it. This is to protect the car head unit from getting blown up, if a electrical short happens, the fuse blows instead.