TM 10-3930-669-20 19.  GLOW PLUG INDICATOR DOES NOT OPERATE (CONT). KNOWN INFO 24 vdc circuits operate. Fuse 4 OK. Indicator wire 30 OK. Relay R6 ground wire OK. Indicator ground wire OK. Wire 7 OK. Terminal 85 ground wire OK. Relay R6, wire 7, terminal 30 OK. Relay R6, wire 30, terminal 87 OK. Wire 31 OK. POSSIBLE PROBLEMS Wire 29 faulty. Glow plug switch faulty. KNOWN INFO 24 vdc circuits operate. Fuse 4 OK. Indicator wire 30 OK. Relay R6 ground wire OK. Indicator ground wire OK. Wire 7 OK. Terminal 85 ground wire OK. Relay R6, wire 7, terminal 30 OK. Relay R6, wire 30, terminal 87 OK. Wire 31 OK. Wire 29 OK. POSSIBLE PROBLEMS Glow plug switch faulty. TEST OPTIONS Voltage test. STE/ICE-R #89. REASON FOR QUESTION If 22 to 24 vdc are not present, wire 29 is faulty. TEST OPTIONS Continuity test. STE/ICE-R #91. REASON FOR QUESTION If continuity is not present, glow plug switch is faulty.  If glow plug switch is OK, wire 31 is faulty. 2-240