TM-9-2320-283-20-1

TRUCK TRACTOR, LINE HAUL, 50,000 GVWR, 6X4, M915A1

TECHNICAL MANUAL; ORGANIZATIONAL MAINTENANCE PART 1 OF 3

DECEMBER 1983
TM-9-2320-283-20-1

  TM-9-2320-283-20-1 - Page 62 of 926

TM 9-2320-283-20-1
PRINCIPLES OF OPERATION.
1-15.
ELECTRICAL SYSTEM (Continued).
c.
Service Lighting System (Continued).
(4)
Backup Lamps.
When the operator places the transmission shift lever in REVERSE position (R), the reverse switch closes.
When
blackout
toggle switch is in NORMAL position and ignition switch is in ON position, the circuit is energized to illuminate
backup bulb in each taillamp assembly.
BATTERY PACK.
Consists of four, 12-volt, maintenance free batteries.
Two batteries
are wired in parallel
in each set.
Each set
is connected in series
for 24-volt
output.
Battery pack is used for both 12-volt and 24-volt output.
IGNITION SWITCH.
Supplies 24-volt to relay (RY-9), which in turn provides 12-volt power to electrical system, including
backup lamp circuit.
RELAY (RY-9).
Energized by 24-volts from ignition switch.
When energized, RY-9 supplies 12-volt power to circuit
breaker (CB-3).
CIRCUIT BREAKER (CB-3).
Protects electrical components of backup switch circuit by opening when load exceeds 20
amperes.
May be manually reset by pressing CB-3 button in.
REVERSE SWITCH.
Normally open contacts.
When closed, it receives 12-volt battery power through circuit breaker CB-
3 and supplies power through normally closed contacts of relay RY-7 to energize backup lamps in taillamp assemblies.
RELAY (RY-7).
Normally closed contacts are opened by 12-volt
power when blackout toggle switch is placed to
BLACKOUT position.
This prevents the backup lamps from coming on whenever the blackout toggle switch is in
BLACKOUT mode.
TAILLAMP (BACKUP LAMP).
Each assembly contains two bulbs:
a taillamp, turn signal, and stoplamp bulb that contains
two filaments; and a backup bulb that contains one filament.
When the backup switch closes, the backup lamp
illuminates.
CIRCUIT BREAKER
(CB-5).
Protects electrical components of relay RY-7 circuits by opening when load exceeds 20
amperes.
May be manually reset by pressing CB-5 button in.
1-42


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