On April 10, 1997, about 1426 eastern daylight time, a Navion A, N40FL, registered to Piggy Bank Motors Company, was substantially damaged by fire after landing at the Quincy Municipal Airport, Quincy, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the maintenance test flight. The private-rated pilot, the sole occupant, was not injured. The flight originated about 5 minutes earlier. The pilot stated to an FAA inspector that he intended to remain in the traffic pattern after takeoff and while on final approach, he smelled what he thought was an electrical fire and felt heat by his legs. He landed and after stopping the airplane, fire erupted in the cockpit. He then exited the airplane and bystanders extinguished the fire using water. According to the FAA inspector, the airplane had been to the facility for an annual inspection and reportedly no work was performed to the instrument panel. The mechanic who performed the annual inspection reported using the airplane manufacturers checklist. The mechanic also stated that postaccident examination of the airplane revealed electrical arching at the firewall where the electrical cable from the battery relay to the starter relay transits through. The battery in the airplane is located aft of the aft seat on the left side of the airplane.