0003
TM 1-1740-221-13&P&P
THEORY OF OPERATION - (CONTINUED)
HEADLIGHT CIRCUIT
Power is applied through a 20 amp fuse (12FU) to the headlight switch (SW3) located on the dash panel. With
the headlight switch in the on position power is applied through the headlight dimmer switch to turn on either the
high or low beam lights. If the dimmer switch is in the high beam position power is also applied to the high beam
indicator (PL4) located on the dash panel.
PARKING LIGHTS
Power is applied through a 20 amp fuse (12FU) to the headlight switch (SW3) located on the panel. With the
headlight switch on power is applied to both right and left front parking lights.
TAIL LIGHTS
Power is applied through a 20 amp fuse (13FU) to the lower portion of the headlight switch (SW3). With the
headlight switch on power is applied to the left and right rear tail lights.
GAUGE LIGHTS
Power is applied through a 20 amp fuse (13FU) to the gauge light dimmer rheostat (FO-1, Line 60) located on the
dash panel. The uses the rheostat to light up the dash panel gauges during night operations.
BRAKE AND TURN SIGNAL LIGHTS
Power is applied through a 20 amp fuse (13FU) to the service brake stoplight switch and to the lasher (turn signal)
relay. When the brake pedal is depressed the normally open stoplight switch (LS-SL) is closed and will illuminate
the left and right rear brake lights through the directional turn signal switch (SW-5).
The turn signal lasher relay receives power from the 20 amp fuse (13FU) and operates the appropriate turn
signals through the turn signal switch (SW-5).
BACKUP ALARM (WARNING HORN)
When the transmission gear shifter is placed in the reverse position, power is applied through the shifter assembly
to the backup alarm to alert personnel of the hazard.
REVERSE LIGHTS (BACKUP)
When the transmission gear shifter is placed in the reverse position, power is applied through the shifter assembly
to diode REC1 (Figure 2FO-1, line 72). Power applied to the anode of REC1 forward biases the diode allowing
the reverse lights to illuminate.
WORK LIGHTS
Power is applied through a 20 amp fuse (13FU) to the work light switch (SW6) located on the dash panel. When the
work light switch is turned on power is applied to the work lights at the rear of the vehicle for night time operations.
END OF WORK PACKAGE
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