What was found
EN ROUTE FROM EDDF TO OKBK, THE MAIN CARGO COMPART SMOKE DETECTION LIGHT ILLUMINATED ACCOMPANIED BY THE WARNING HORN. THE CREW SILENCED THE HORN AND THE A/C DIVERTED TO IST FOR AN UNEVENTFUL LANDING. THE CARGO WAS OFF LOADED AND INSPECTED WITH NO EVIDENCE OF A FIRE. THE CREW REPORTED THE A/C WAS LOADING IN HEAVY RAINS IN EDDF. MX INSPECTED THE SMOKE DETECTION SYSTEM WHICH REVEALED MOISTURE WITHIN THE SYSTEM. MX CLEANED AND DRIED ALL SMOKE DETECTORS AND A SUCCESSFUL OPERATIONAL TEST WAS PERFORMED IAW WITH THE MX MANUAL. THE CARGO WAS LOADED AND THE A/C RETURNED TO SERVICE.