TM 9-2320-364-20-2 2-1564 45.  TRAILER BLACKOUT STOPLIGHTS DO NOT OPERATE (CONT). Trailer stoplights operate,   indicating wire 1435 at   connector MC15 OK. 22 to 28 vdc supplied to   connector MC15. Wire 1676 OK. Wire 1678 OK. Wire 1435 OK. Trailer blackout stoplight relay   R13 faulty. Wire 1678C faulty. KNOWN INFO POSSIBLE PROBLEMS TEST OPTIONS REASON FOR QUESTION Voltage test. STE/ICE-R #89. If 22 to 28 vdc are not present at wire 1678C, blackout stop- light relay R13 is faulty. YES NO Replace trailer blackout stoplight relay R13 (Para 7-95). Verify repair, go to Step 6 of this Fault. 5. Are 22 to 28 vdc measured on wire 1678C at trailer blackout stoplight relay R13, terminal 87? Repair wire 1678C (see schematic Fig 2-35) or notify DS Maintenance. Verify repair, go to Step 6 of this Fault. 4. Repair wire 1435 (see schematic Fig 2-35) or notify DS Maintenance. Verify repair, go to Step 6 of this Fault. YES NO Trailer stoplights operate,   indicating wire 1435 at   connector MC15 OK. 22 to 28 vdc supplied to   connector MC15. Wire 1676 OK. Wire 1678 OK. Wire 1435 faulty. Trailer blackout stoplight relay   R13 faulty. Wire 1678C faulty. KNOWN INFO POSSIBLE PROBLEMS TEST OPTIONS REASON FOR QUESTION Continuity test. STE/ICE-R #91. If trailer blackout stoplight relay R13 is not grounded through wire 1435, relay will not operate. WARNING WARNING Is continuity measured on wire 1435 between trailer blackout stoplight relay R13, terminal 85 and a known good ground? Read   WARNING on Page 2-1565 Read   WARNING on Page 2-1565