As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ACFT TAXIED TO POSITION, CREW NOTICED A STRONG ODOR AND REALIZED THAT SMOKE WAS COMING FROM AN OVERHEAD PANEL AT THE FLIGHT ENGINEERS STA. ACFT WAS SHUTDOWN AND TOWED BACK TO RAMP. MX IDENTIFIED THE PROBLEM TO BE A FAULTY EXTERNAL POWER SWITCH. SWITCH WAS REPLACED AND ACFT RETURNED TO SERVICE.