Understanding And Troubleshooting Electrical Systems; Basic Electrical Theory; How Does Electricity Work: The Water Analogy - Ford Ranger Maintaince And Repair Manual

UNDERSTANDING AND TROUBLESHOOTING
ELECTRICAL SYSTEMS

Basic Electrical Theory

For any 12 volt, negative ground, electrical system to operate, the electricity must travel in a complete circuit.
This simply means that current (power) from the positive (+) terminal of the battery must eventually return to
the negative (−) terminal of the battery. Along the way, this current will travel through wires, fuses, switches
and components. If, for any reason, the flow of current through the circuit is interrupted, the component fed by
that circuit will cease to function properly.
Perhaps the easiest way to visualize a circuit is to think of connecting a light bulb (with two wires attached to
it) to the battery−one wire attached to the negative (−) terminal of the battery and the other wire to the positive
(+) terminal. With the two wires touching the battery terminals, the circuit would be complete and the light
bulb would illuminate. Electricity would follow a path from the battery to the bulb and back to the battery. It's
easy to see that with longer wires on our light bulb, it could be mounted anywhere. Further, one wire could be
fitted with a switch so that the light could be turned on and off.
This example illustrates a simple circuit. When the switch is closed, power from the positive (+)
battery terminal flows through the fuse and the switch, and then to the light bulb. The light
illuminates and the circuit is completed through the ground wire back to the negative (−) battery
terminal. In reality, the two ground points shown in the illustration are attached to the metal
frame of the vehicle, which completes the circuit back to the battery
The normal automotive circuit differs from this simple example in two ways. First, instead of having a return
wire from the bulb to the battery, the current travels through the frame of the vehicle. Since the negative (−)
battery cable is attached to the frame (made of electrically conductive metal), the frame of the vehicle can
serve as a ground wire to complete the circuit. Secondly, most automotive circuits contain multiple
components which receive power from a single circuit. This lessens the amount of wire needed to power
components on the vehicle.

HOW DOES ELECTRICITY WORK: THE WATER ANALOGY

Electricity is the flow of electrons−the subatomic particles that constitute the outer shell of an atom. Electrons
spin in an orbit around the center core of an atom. The center core is comprised of protons (positive charge)
and neutrons (neutral charge). Electrons have a negative charge and balance out the positive charge of the
protons. When an outside force causes the number of electrons to unbalance the charge of the protons, the

UNDERSTANDING AND TROUBLESHOOTING ELECTRICAL SYSTEMS

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