What was found
FLIGHT CREW REPORTED SPEED BRAKES WOULD NOT DEPLOY ON DESCENT GOING THROUGH 9000 FT AT 250 KIAS. SPEED BRAKES EVENTUALLY DEPLOYED AFTER CYCLING SPEED BRAKE CONTROL SWITCH SEVERAL TIMES. TROUBLESHOT SYS, FOUND HIGH INTERNAL RESISTANCE IN THE S156 SPEED BRAKE RETRACT LIMIT SWITCH. REPLACED THE S156 SWITCH WITH A NEW SWITCH, SPEED BRAKE SYS CHECKS IAW SERIES MM 27-60-00 WERE OK, NO FAULTS NOTED. RECOMMEND AIRFRAME MFG INVESTIGATE WHETHER AN ISOLATED FAULT, OR IF THERE MIGHT BE A PROBLEM WITH A SPECIFIC LOT OF SWITCH ASSY.