What was found
(CAN) ON TAKE-OFF, LANDING GEAR CAUTION LIGHT ILLUMINATED. CREW ELECTED TO RETURN, AND PERFORMED ALTERNATE GEAR EXTENSION, AND THE LT MLG DOOR AMBER LIGHT STAYED ILLUMINATED. LANDING WAS COMPLETED WITH NO FURTHER INCIDENT. DURING MAINTENANCE TROUBLE-SHOOT, THE PSEU WAS CHANGED, THE LT MLG DOOR SEQUENCE VALVE WAS REPLACED, AND WIRING FROM PSEU TO LT SEQUENCE VALVE WAS REPLACED. GEAR SWING AND TEST FLIGHT WERE COMPLETEDWITH NO FURTHET RE-OCCURRANCE.