As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING RUN-UP, AMPS FULL LOAD CHECK, SPARKS WERE SEEN FROM PILOTS SIDE WHEN LIGHTS SWITCHED ON. FAINT ODOR OF SMOKE AND NAV. LIGHT C/B POPPED. TURNED LIGHT SWITCH OFF. SPARKS SEEN FROM PARKING BRAKE AREA. ACFT RETURNED TO RAMP W/O FURTHER PROBLEMS. MX FOUND THE NAV LIGHT SWITCH (PN:TA201-TW-B/ALT.: S2160-1) UNSERVICEABLE. SWITCH REPLACED IAW INTERNAL WORK PROCEDURES. TESTED UNDER FULL LOAD AND FOUND SERVICEABLE.