What was found
ON 2/12/2015 WHILE ON GND PREPARING FOR A RETURN FLIGHT, BEFORE ENG START, FLIGHT CREW MEMBERS WERE CONDUCTING PREFLIGHT CHECKS ON ACFT SYSTEMS. FLIGHT CREW NOTICED AUTOPILOT WOULD NOT PASS INTERNAL CHECKS & THE RED PITCH TRIM LIGHTS WERE ILLUMINATED ON THE AUTOPILOT PANEL. FURTHER INVESTIGATION REVEALED THE SEC PITCH TRIM CB WAS OPEN. FLIGHT CREW REFERRED TO CHECKLIST & TRIED CLOSING CB ONLY TO HAVE IT TRIP WITHIN A FEW SECONDS. FLIGHT CREW REVIEWED CHECKLIST, MEL & AFM, DETERMINED THAT TRIM SYS COULD NOT BE DEFERRED. DISCUSSED ISSUE WITH MANUFACTURER & SUSPECT PITCH TRIM ADAPTER PN 065-5046-01. ACFT WAS ISSUED SPECIAL FLIGHT PERMIT TO BE REPOSITIONED FOR TROUBLESHOOTING & REPAIRS.