What was found
PTU SWITCH LIGHT STAYED ILLUMINATED AFTER TAKEOFF. RETURNED TO FIELD. LANDING UNEVENTFUL. TESTED RELAYS IN PTU AUTO SYSTEM. RELAY 2921-1-K3 FAILED TO CLOSE WHEN COMMANDED. REPLACED RELAY IAW 20-30-16-960-801. RELAY OPS GOOD IAW TABLE 201 OF 24-50-60-710-804. PTU FUNCTIONAL TESTED GOOD SEVERAL TIMES IAW 29-11-61-720-801. CHECKED GOOD. REPLACED PTU SELEECTOR VALVE IAW 29-11-66-000-801, 29-11-66-400-801. OPS AND LEAK CHECKED GOOD. RETURNED TO SERVICE.