TROUBLESHOOTING THE M998 ELECT SYST. - OD1617 - LESSON 1/TASK 1
In order to effectively troubleshoot any of the various HMMWV
components and systems, maintenance personnel must first understand
the operation of the system they are troubleshooting. The purpose of
this task is to introduce the student to these components, and to the
operation of the HMMWV electrical system.
The electrical system on any vehicle serves an indispensable purpose.
Without the electrical system, most vehicles could not be started.
Also, it would be impossible to operate the vehicle at night since
there would be no external or internal lighting. Additionally, there
would be no way for the operator to monitor such vehicle operations
as speed, engine coolant, oil pressure, and a multitude of other
items that must be constantly checked to ensure correct vehicle
operation. In this lesson, the characteristics and operation of the
HMMWV electrical system will be discussed.
Electrical System Components. The HMMWV electrical system is a
24 volt system capable of submerged operation during fresh or
It provides for starting the vehicle, charging
the batteries, and operating the controls, gages, and accessory items
peculiar to this vehicle.
In the paragraphs that follow, the components that comprise the
electrical system on the HMMWV will be discussed.
consists of 15 components: batteries, alternator, starter, wiring
harness, protective control box, circuit breakers, instruments,
heater/defroster, slave receptacle, and trailer receptacle.
(1) Batteries. Two 12 volt batteries are connected in series to
supply the 24 volt current required to start and operate the engine
The batteries are mounted in an enclosed
compartment under the right front crew seat. They are secured by a
holddown clamp and are joined by a negative to positive jumper cable.
The negative terminal is connected to the vehicle ground, while the
positive terminal is connected to the vehicle starter. The batteries
supply the necessary power required to start the vehicle, and the
circuit is identified as circuit 6A. This circuit connects