TM 9-2320-273-20
2-47. BACKUP LAMPS.
When the operator places the gear ratio selector lever in reverse position (R1 or R2), air pressure
within the transmission closes backup switch. When operation lamp switch in NORMAL position and
engine run switch ON, the circuit is energized to illuminate each backup bulb in tail lamp assembly.
1. BACKUP SWITCH. The switch is normally open. When closed, it receives 12-volt battery
power through circuit breaker CB-5 and supplies power through normally closed contacts of
relay K7 to energize backup lamps in tail lamp assemblies.
2. RELAY (K7). The relay is normally closed. When the operation lamp switch is placed to
BLACKOUT position, 12-volt power is supplied to coil of K7, energizing the relay, and opens
the contacts. This prevents the backup lamps from coming on whenever the operation lamp
switch is in BLACKOUT mode.
3. ClRCUIT BREAKER (CB-5). Protects electrical components of backup switch circuit by
opening when load exceeds 20 amps. Automatically recycles until overload is removed.
4. ClRCUIT BRAKER (CB-2). Protects electrical components of relay K7 circuits by opening
when load exceeds 20 amps. Automatically recycles until overload is removed.
5. TAIL LAMP. Each assembly contains two bulbs: A tail, turn signal, and stop lamp bulb
which contain two filaments and backup bulb which contains one filament. When the backup
switch closes, the backup lamp illuminates.
6. OPERATION LAMP SWITCH. Two-position switch for NORMAL AND BLACKOUT modes
of operation. In this circuit, the switch is used to prevent operation of the backup lamp. In
BLACKOUT position, 12-volt power from circuit breaker CB-2 passes through the switch and
energizes coil of relay K7, thus preventing the backup lamps from possibly coming on.
7. ENGINE RUN SWITCH. This switch controls 12-volt power to the backup switch through
circuit breaker CB-5. When the switch is off the backup lamp circuit is de-energized.
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