What was found
IN CRUISE WITH IRS OFF,(ON DMI NR 22820) IRS FAULT ON DC, DC FAIL LIGHTS INTERMITTENTLY ON AND OFF. LATER SMELL OF ELECTRICAL SMOKE EVIDENT IN THE COCKPIT. COMPLIED WITH CHECK LIST, FOUND LT IRU AC C/B TRIPPED. PULLING LT IRU DC C/B AND USING ALT EQUIPMENT COOLING CLEARED SMOKE. REMOVED AND REPLACED LT IRU AND OPS CHECKED NORMAL IAW MM 34-21-01, THIS CLEARS DMI NR 22820 AND PLACARD REMOVED.