Ford Explorer, Maintaince And Repair Manual, Page: 653 / 1119

Relays are composed of a coil and a switch. These two components are linked together so that when one operates, the
other operates at the same time. The large wires in the circuit are connected from the battery to one side of the relay
switch (B+) and from the opposite side of the relay switch to the load (component). Smaller wires are connected from the
relay coil to the control switch for the circuit and from the opposite side of the relay coil to ground
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LOAD
Every electrical circuit must include a "load'' (something to use the electricity coming from the source).
Without this load, the battery would attempt to deliver its entire power supply from one pole to another. This
is called a "short circuit." All this electricity would take a short cut to ground and cause a great amount of
damage to other components in the circuit by developing a tremendous amount of heat. This condition could
develop sufficient heat to melt the insulation on all the surrounding wires and reduce a multiple wire cable to
a lump of plastic and copper.
WIRING & HARNESSES
The average vehicle contains meters and meters of wiring, with hundreds of individual connections. To
protect the many wires from damage and to keep them from becoming a confusing tangle, they are organized
into bundles, enclosed in plastic or taped together and called wiring harnesses. Different harnesses serve
different parts of the vehicle. Individual wires are color coded to help trace them through a harness where
sections are hidden from view.
Automotive wiring or circuit conductors can be either single strand wire, multi−strand wire or printed
circuitry. Single strand wire has a solid metal core and is usually used inside such components as alternators,
motors, relays and other devices. Multi−strand wire has a core made of many small strands of wire twisted
together into a single conductor. Most of the wiring in an automotive electrical system is made up of
multi−strand wire, either as a single conductor or grouped together in a harness. All wiring is color coded on
the insulator, either as a solid color or as a colored wire with an identification stripe. A printed circuit is a thin
film of copper or other conductor that is printed on an insulator backing. Occasionally, a printed circuit is
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