TROUBLESHOOTING THE M998 ELECT SYST. - OD1617 - LESSON 1/TASK 1
(5) Protective Control Box (PCB).
The PCB used on the HMMWV is
similar to the control boxes used on other military vehicles, with an
added provision for the glow plugs. The functions of the PCB are to
energize the glow plugs, prevent battery polarity reversals, energize
the starter solenoid, and prevent reengagement while the engine is
The PCB is mounted behind the instrument panel in the
driver's compartment and is serviced only as an assembly.
(6) Circuit Breakers.
Two standard military circuit
provide overload protection on the HMMWV. These are of the
cycling, and automatic reset type.
Circuits critical to
operation are not run through circuit breakers; these
starter, alternator, and radio power supplies. The circuit
are located on a panel below the dashboard on the driver's
(7) Driver's Compartment.
The driver's compartment contains
vehicle control indicators, and a removable instrument cluster. The
cluster contains gages that monitor the engine temperature, oil
pressure, fuel level, vehicle speed/mileage, and battery voltage
through sending units, except the speedometer and voltmeter. Also on
the removable cluster is the hi-beam indicator.
The WAIT TO START
and BRAKE indicators are located on the dash to the left of the
(8) Brake Indicator.
The BRAKE indicator illuminates when a
system hydraulic failure occurs or when the parking brake is engaged.
proportioning valve switches if either or both switches are closed.
(9) Vehicle Lighting System.
The history of motor vehicle
lighting parallels the history of the lighting of houses and
buildings, with oil and gas lamps having been used in the early motor
vehicles. With the development of a satisfactory electrical system,
electric lighting has become the standard means of lighting motor
system in which a main switch controls the service headlights,
blackout lights, directional signals and the panel lights. When the
panel is illuminated, a lamp in the transmission quadrant illuminates
the position of the shift lever