What happened
Prior to departure, the pilot observed that the battery appeared weak and noted that the ammeter was neither charging nor discharging. After charging the battery for 30 minutes, the pilot decided to fly to another airport to have a mechanic inspect the aircraft.
During the flight, the pilot noticed the engine was running rough. Upon checking both magnetos, the pilot found that selecting the left magneto resulted in continued engine roughness. Additionally, the fuel pressure was low, but the pilot continued toward the destination. Eventually, both magnetos began to run rough, making it impossible to maintain altitude. The pilot performed an emergency landing on a highway. While maneuvering the aircraft to avoid oncoming traffic, the plane struck a road sign, resulting in substantial damage.
The investigation
An examination of the engine revealed that the P-lead had broken off of the right magneto. It was determined that the P-lead had been rubbing against a bracket located aft of the lead prior to its failure.