AC^DC "BACK IN BLACK"

BRIAN JOHNSON AS ALOT OF U KNOW WASN'T AC^DC's FIRST LEAD SINGER, IN FACT HE REPLACED THE LATE GREAT BON SCOTT AFTER HIS UNTIMELY DEMISE. DOES ANYONE KNOW WHAT JOB MR. JOHNSON HELD BEFORE TAKING OVER SINGING FOR A BIG ROCK N ROLL BAND?