What was found
CABIN ALTITUDE WAS NOTED AT 16,000 FT (DUE IMPACT - DAMAGE TO FUSELAGE) IN FLIGHT - CREW STATED USING SUPPLEMENTAL OXYGEN AT THIS POINT. CABIN ALTITUDE WARNING DID NOT FUNCTION, WARNING LIGHT SHOULD COME ON AT 12,250 FT. REPLACED DEFECTIVE SWITCH. WARNING SWITCH FOR CABIN PRESSURIZATION/ ALTITUDE, DID NOT FUNCTION DURING PRESSURIZATION LOSS.