What was found
UPON APPROACH TO LANDING, WE EXTENDED THE LANDING GEAR. WE RECEIVED THE LANDING GEAR DISAGREE CAS MESSAGE FOR THE LEFT MAIN GEAR ALONGSIDE THE YELLOW CROSS ON THE INDICATION. AFTER ABANDONING THE APPROACH AND CIRCLING THE AIRPORT APPROXIMATELY 45 SECONDS AFTER EXTENSION WAS ASKED, 3 GREEN ILLUMINATED AND REMAINED ON THE REMAINDER OF THE FLIGHT. WE DID NOT RECYCLE THE LANDING GEAR. REMOVED FAULTY LT MLG UPLOCK SWITCH WITH HARNESS AND INSTALLED A CUSTOMER SUPPLIED NEW UPLOCK SWITCH WITH HARNESS. ALL WORK ACCOMPLISHED IAW AMM 32-30-05. PERFORMED A SUCCESSFUL FUNCTIONAL TEST OF THE MLG EXTENSION AND RETRACTION. WORK ACCOMPLISHED IAW AMM 32-01-00.