1 - A CAR STEREO / IF IT IS PROTECT MAY BE A PASSWORD USED FOR ANTITHEFT.
2 - HOME STEREO / SAYS PROTECT , CHECK WIRING AGAIN
TRY HOOKING UP ONE SPEAKER AT A TIME TO FIND OUT WHICH ONE IS BLOWN.
IF THAT DOES NOT FIX THE ISSUE, YOU HAVE INTERNAL PROBLEMS
JESSE P NELSON, June 2007