What was found
ACFT OPERATOR TAXIED TO RUN UP AREA AND PERFORMED PREFLIGHT CHECKS. NOTED AUTOPILOT WOULD NOT PASS PREFLIGHT TEST. RETURNED ACFT TO SERVICE HANGAR. DURING TROUBLESHOOTING PROCESS, FOUND THAT PIN F AT TERMINAL BLOCK 290-02 WAS NOT FULLY SEATED. THIS CAUSED AN OPEN CIRCUIT FOR AUTOPILOT DISCONNECT LINE AND FAILED THE TEST. AFTER INFORMING OPERATOR, THEY MENTIONED THAT THEY HAVE HAD SOME INSTANCES OF CLEAR AIR AUTOPILOT DISCONNECTS AS WELL PREVIOUSLY. RESEATED THIS PIN AND AUTOPILOT PASSED PREFLIGHT TEST SATISFACTORILY. WE HAVE FOUND INSTANCES OF LOOSE PINS IN TERMINAL BLOCKS ( VARIOUS SYS) OCCASIONALLY ON OTHER ACFT. THIS AREA SHOULD BE CHECKED CLOSELY WHEN TROUBLESHOOTING HARD TO FIND PROBLEMS.