As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A NIGHT FLIGHT, THE AIRSPEED, ALTIMETER & CLOCK BACK LIGHTING WENT FULL BRIGHT. ADJUSTING THE LIGHTING RHEOSTAT HAD NO EFFECT. THE CREW NOTICED A BURNING ELECTRICAL SMELL IN THE COCKPIT. ACFT RETURNED TO BASE WITH NO FURTHER INCIDENT. LIGHTING POWER SUPPLY FOUND TO BE DEFECTIVE & REPLACEMENT ORDERED.