Short circuit: There may be a short circuit in the wiring between the CD player and the tail lights. This could be caused by damaged or pinched wires, or by loose connections. Inspect the wiring for any signs of damage or loose connections, and repair or replace as necessary.
Faulty CD player: The CD player itself may be faulty and drawing too much power, causing the fuse to blow. Try disconnecting the CD player and see if the fuse still blows. If it doesn't, then the CD player is likely the culprit and will need to be repaired or replaced.
Overloaded circuit: The tail light fuse may be overloaded if there are too many devices connected to the same circuit. Check to see if any other devices are connected to the same circuit as the tail lights and disconnect them to see if the fuse still blows. If it doesn't, then one of the other devices is likely drawing too much power and will need to be repaired or replaced.
Blown fuse: The fuse itself may be blown and simply need to be replaced. Check the fuse to see if it is blown and replace it if necessary.
