As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) PILOTS HAVE BEEN REPORTING INTERMITTENT SULPHUR SMELL IN THE ACFT. WHILE TROUBLESHOOTING, THE MECHANIC NOTICED THAT THE APU DOOR WAS OPEN AND APU MASTER AS OFF. WHEN THE APU SWITCH WAS CYCLED TO CLOSE THE DOOR, SPARKS STARTED TO APPEAR NEXT TO START SWITCH IN THE COCKPIT. UPON REMOVAL OF THE CONTROL BOX, IT WAS NOTICED THAT THE RUBBER SLEEVE AROUND THE START SWITCH WAS MELTED AND THERE WERE SIGNS OF BURNING ON THE WIRES COMING OUT OF THE SWITCH.