Group 30 Electrical System—VNL, VNM
Design and Function
Design and Function
General Circuit Information
Circuit Malfunctions
In an electrical circuit, current completes a path from its source through the compo-
nent(s), and then back to its source. If it starts at the battery, it must return to the
battery. Current will return to the source even in circuits that are not operating properly.
There are three electrical conditions that cause an inoperative circuit; these conditions
are known as an "open circuit," a "short circuit" and a "grounded circuit."
Open Circuit
Whenever there is a complete break or interruption in the
normal current path, such as a break in wiring from the
source of power to the electrical unit or within the unit
itself, current will not flow. In a circuit, current normally
travels through the wires or cables, to switches and
electrical unit(s), such as the starter solenoid and cranking
motor, through another wire to ground and back to the
source.
A break anywhere along this route results in an open
circuit and the complete loss of power. In a sense, the
break is a very high resistance in the circuit. However,
the symptoms will appear somewhat different than the
typical high resistance because there is no current flow.
An ammeter will not register at all because there cannot
be current flow through an open circuit. A voltmeter,
depending on where it is placed in relation to the open
circuit, may or may not give a reading. The proper use of
meters is covered later in this manual.
Any abnormal resistance reduces the current flow in a
circuit and leaves the unit intermittent or non-functioning.
An open or high-resistance circuit may occur as the
result of a broken wire within the wiring harness, loose
connections at terminals of electrical units, broken wiring
within the units, or poor ground connections between the
unit and ground. Open circuits, depending on the type
and location of the open, can easily create a shorted or a
grounded circuit condition.
W3000489
9
