As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PUSHED THE STARTER BUTTON FOR THE FIRST FLIGHT AND THERE WAS A LOUD POP AND SPARKS FOR THE LT SIDE OF THE LOWER INSTRUMENT PANEL. MAINTENANCE FOUND THE BATTERY RELAY GROUND WIRE ON THE AIRFRAME SIDE LOOSE, REMOVED GROUND AND CLEANED TERMINAL AND REINASTALLED GROUND WIRE. THE AIRCRAFT WAS GROUND RUN AND OPS CHECKED GOOD.