What was found
AT CRUISE WITH AUTOPILOT A ENGAGED WE SLOWED DOWN FROM M .77 TO M .69 AT FL400. ACFT PITCH NOSE DOWN AS WE SLOWED. AUTOPILOT WAS MANUALLY DISCONNECTED TO CORRECT ALTITUDE ACFT WAS OUT OF TRIM IN NOSE DOWN. TRIM WAS 5 UNITS FROM CLIMBOUT UNTIL MANUALLY RETRIMMED. MANUALLY RETRIMMED TO 6 UNITS AND RE-ENGAGED AUTOPILOT. NO STAB TRIM CHANGE WAS NOTED DURING ENTIRE 2.5 HOUR CRUISE SEGMENT. STAB OUT OF TRIM LIGHT CAME ON SLOWING 250- 190 SPEED AT 12000 FEET. GROUNDED - YES. FOUND D2257 DISCONNECTED ON COLUMN SWITCHING MODULE (M1201). RECONNECTED CONNECTOR. PERFORMED REPAIR CONFIRMATION IAW FIM 22-13 TASK 808 STEP F. OPS CHECKS GOOD.