What was found
OWNER COMPLAINED OF FLUCTUATING AMMETER AND LIGHTS. ALTERNATOR, REGULATOR, AND OVERVOLTAGE REGULATOR HAD BEEN PREVIOUSLY REPLACED. AFTER BYPASSING ALTERNATOR SWITCH, FLUCTUATIONS WENT AWAY. PROBLEM CAUSED BY AGE OF SWITCH. SUBMITTER STATED HAVE SEEN THIS ON OTHER AIRCRAFT. ONE WAY TO PREVENT PROBLEM COULD BE TO REPLACE UNIT AFTER 2,000 HOURS.