What was found
FLIGHT 15976 (MER) TO (GCN): WHILE CLIMBING THROUGH 11,000FT THE AUTO-PILOT ENGAGED WITHOUT THE CREW SELECTING THE SYSTEM ON. NEITHER CONTROL WHEEL A/P DISCONNECT SWITCH WOULD DISENGAGE THE AUTO-PILOT. THE FIRST OFFICER HAD TO HOLD DOWN THE DISCONNECT BUTTON CONTINUOUSLY ON THE AUTO-PILOT CONTROL PANEL APP-65A TO DEACTIVATE THE SYSTEM. THE AIRCRAFT RETURNED TO MER AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE APP-65A CONTROL PANEL WAS WET WITH WHAT APPEARED TO BE COFFEE. THE CONTROL PANEL WAS REPLACED, THE AIRCRAFT TEST FLOWN WITH THE SYSTEM CHECKING GOOD. AIRCRAFT RETURNED TO SERVICE.