What was found
DURING POST ENGINE START/PREFLIGHT CHECKS, NOTED THE "SPEED BRAKE EXTENDED" ANNUNCIATOR FAILED TO ILLUMINATE. VISUAL INSPECTION CONFIRMED THE BRAKES EXTENDED, & "HYD PRESS" LIGHT EXTINGUISHED CONFIRMING SYS HAD COMPLETED IT’S CYCLE. ANNUNCIATOR LIGHT TEST PERFORMED & LIGHT FUNCTIONED NORMALLY. SPEED BRAKES CYCLED AGAIN WITH NO CHANGE. ENGINES SHUTDOWN. INVESTIGATION REVEALED A WIRE BUNDLE CHAFING ON SECONDARY WING STRUCTURE INSIDE RT AFT WING APPROX WS 24. CHAFE WORN THROUGH PROTECTIVE SHIELDING & THROUGH WIRE INSULATION. SUBSEQUENT ARC MELTED & OPENED WIRE. CIRCUIT BREAKER NOT POPPED & NO REPORTS OF BREAKER BEING POPPED BY PREVIOUS CREW. CIRCUIT BREAKER INSPECTED, NO DEFECTS NOTED & OPERATED NORMALLY WHEN MANUALLY PULLED. WIRE REPAIRED USING A MANUAL SPLICE. BUNDLE REWRAPPED & POSITIONED TO PREVENT FURTHER CHAFING. NO DAMAGE TO STRUCTURE NOTED. A GROUND OPS CHECK OF SYS PERFORMED NORMALLY & ACFT RETURNED TO SERVICE.