2-71
TM 9-2320-280-20-1
2-21. ELECTRICAL TESTS
Most of the electrical circuits in the vehicle are included in one of the major systems covered by
this manual. This is a top level paragraph to help you pick the right one. A number of
schematics are also included to help you find the problem. If you go through the flowchart and
can’t solve the problem, use the schematics to find wires which may be causing trouble.
The Electrical System consists of the batteries, which produce electrical power by a chemical
reaction between the lead plates and the electrolyte solution (a mixture of acid and water).
This power is carried by wires and cables to those parts of the vehicle which require electrical
power. The batteries get recharged by the alternator, which generates electrical power by
using some of the engine’s mechanical power, produced when the engine is running. If you
are not too confident about electrical concepts and terminology, you should read Paragraph
2-16, page 2-39.
All electrical systems require a connection to ground (called grounding), which is the
completion of the circuit to the battery negative. Pages 2-66, 2-67 and 2-68 are diagrams of
the grounding. If your vehicle exhibits strange symptoms that seem to defy all efforts to fix
them, the vehicle may have a grounding problem. Grounding problems cause strange
symptoms usually because more than one circuit is using the same ground, or because a
circuit has more than one ground. For example, looking at the body ground diagram, if wire
58D (a ground for the instruments) is disconnected from the left side cylinder head, the
instruments may still function due to the separate ground, but they would probably be erratic
and inaccurate. Usually the problem will be a loose or corroded connection between the circuit,
through body ground to battery negative terminal. Be sure to check continuity to battery
negative cable rather than simply to the vehicle body or engine block.
After the grounding diagrams are functional flow schematics of the major systems in the
vehicle. The shaded areas are the wires and components of the vehicle master power
distribution. These are designed to help you find the system giving you problems.
