2-27. 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 flow chart and cant 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 engines
mechanical power, produced when the engine is running. If you are not too confident about electrical
concepts and terminology, you should read para. 2-22, page 2-43.
All electrical systems require a connection to ground (called grounding), which is the completion of
the circuit to the battery negative. Pages 2-90, 2-91, and 2-92 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.
VEHICLE MASTER POWER CIRCUIT
FROM ALL SYSTEMS
VEHICLE GROUND SYSTEM