Background
The pilot of the aircraft reported that the engine would not start and suspected a dead spot on the starter. The pilot then requested a mechanic to rotate the propeller to address the issue.
Incident Details
All switches in the cockpit were off except for the battery switch. When the mechanic manually rotated the propeller, the engine started unexpectedly. The rotating propeller struck the mechanic.
Investigation Findings
Examination of the aircraft's ignition wiring revealed that the right magneto 'P' lead was incorrectly connected to the ground terminal. This connection caused the right magneto to be open, or hot, meaning it remained energized even when the ignition switches were in the off position. Normally, the 'P' lead grounds the magneto to prevent spark generation. The incorrect wiring prevented this grounding, allowing the magneto to produce sparks as the propeller was turned, leading to the engine start.