What was found
NR 3 MANIFOLD FAILURE LIGHT ILLUMINATED IN CRUISE AT FL 370. RED TABS FOLLOWED. T/S PER TAFI 36-23-00 FAULT CODE BC/YZ. PROBLEM DUPLICATED WITH OR WITHOUT PNEU SYS NR 3 PRESSURIZED. ACCOMPLISHED NR 3 PNEUMATIC SYSTEM DECAY CHECK PER DC-10 JRH TEST PASSED. WHEN DUPLICATING PROBLEM PNEU PRESSURE SWITCH FAULT BALL WOULD ILLUMINATE ON FAULT INDICATOR WITH FAIL LIGHT. REMOVED AND REPLACED NR 3 PNEUMATIC MANIFOLD FAILURE PRESSURE SWITCH PER MM 36-23-03-4. OPS CHECKED NORMAL. ITEM CLEARED, A/C OK TO CONTINUE.