What was found
CABIN ALTITUDE WARNING HORN 'ON' DURING CRUISE FLIGHT. CABIN ALTITUDE ABOVE 10,000 FEET AT FL 310 AND MANIFOLD AIR PRESSURE LIGHT 'ON'. ABNORMAL CHECKLIST COMPLETED, CONDITION CONTINUED. FOUND R263 WIRE LOOSE TO GND. TIGHTENED, CHECKED AT ENGINE RUN. PRESSURIZATION IN GROUND MODE, FLIGHT MODE ALL SYSTEMS OPS CHECK NORMAL IAW MM 21-30-0, 32-2-0 AND 36-1-2. AIRCRAFT RETURNED TO SERVICE. (M)