What was found
AFTER ROTATION LANDING GEAR FAILED TO RETRACT. EICAS MESSAGE PRESENTED LG AIR/GND FAIL. LANDING GEAR HANDLE WAS STUCK IN THE DOWN AND LOCKED POSITION. AIR RETURN REQUIRED AS GEAR COULD NOT BE CYCLED. NOTE; EICAS MESSAGE EXTINGUISHED AFTER FLAPS SET 22 DEGREES. THERE WERE NO PINS INSTALLED IN THE LANDING GEAR. CORR ACTION- INSPECTED MLG AND NLG PROXIMITY SWITCH CONNECTIONS. FOUND LOOSE CANNON PLUG CONNECTOR TO THE LANDING GEAR SOLENOID VALVE. SECURED CANNON PLUG, AND PERFORMED OPERATIONAL CHECK OF LANDING GEAR. OPS CHECK SATISFACTORY.