1991 1999 ford explorer chilton User Manual

current were to reach the load in the circuit, the surge could burn it out or severely damage it. It can also
overload the wiring, causing the harness to get hot and melt the insulation. To prevent this, fuses, circuit
breakers and/or fusible links are connected into the supply wires of the electrical system. These items are
nothing more than a built-in weak spot in the system. When an abnormal amount of current flows through the
system, these protective devices work as follows to protect the circuit:...

melt. Since this link is very early in the electrical path, its the first place to look if nothing on the
vehicle works, yet the battery seems to be charged and is properly connected.
CAUTION
Always replace fuses, circuit breakers and fusible links with identically rated components. Under no
circumstances should a component of higher or lower amperage rating be substituted.
SWITCHES & RELAYS
Switches are used in electrical circuits to control the passage of current. The most common use is to open and...

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
Click to enlarge
LOAD
Every electrical circuit...

sandwiched between two sheets of plastic for more protection and flexibility. A complete printed circuit,
consisting of conductors, insulating material and connectors for lamps or other components is called a printed
circuit board. Printed circuitry is used in place of individual wires or harnesses in places where space is
limited, such as behind instrument panels.
Since automotive electrical systems are very sensitive to changes in resistance, the selection of properly sized
wires is critical when...

are bent. Make certain that the connectors are properly seated and all of the sealing rings are in place
when connecting leads.
Molded-these connectors require complete replacement of the connector if found to be defective.
This means splicing a new connector assembly into the harness. All splices should be soldered to
insure proper contact. Use care when probing the connections or replacing terminals in them, as it is
possible to create a short circuit between opposite terminals. If this happens to the...

pin connector) that is required for the particular application being tested. In cramped, hard-to-reach areas, it
is advisable to have insulated boots over the jumper wire terminals in order to prevent accidental grounding. It
is also advisable to include a standard automotive fuse in any jumper wire. This is commonly referred to as a
fused jumper. By inserting an in-line fuse holder between a set of test leads, a fused jumper wire can be
used for bypassing open circuits. Use a 5 amp fuse to provide...

circuit. If the test light illuminates, there is power up to that point in the circuit; if the test light does not
illuminate, there is an open circuit (no power). Move the test light in successive steps back toward the power
source until the light in the handle illuminates. The open is between the probe and a point which was
previously probed.
The self-powered test light is similar in design to the 12 volt test light, but contains a 1.5 volt penlight battery
in the handle. It is most often used in...

Ammeter-an ammeter measures the amount of current flowing through a circuit in units called
amperes or amps. At normal operating voltage, most circuits have a characteristic amount of amperes,
called current draw which can be measured using an ammeter. By referring to a specified current
draw rating, then measuring the amperes and comparing the two values, one can determine what is
happening within the circuit to aid in diagnosis. An open circuit, for example, will not allow any
current to flow, so the...

The infinite reading on this multimeter indicates that the circuit is open
This test already assumes the existence of an open in the circuit and it is used to help locate the open portion.
Isolate the circuit from power and ground.
1. 
Connect the self-powered test light or ohmmeter ground clip to the ground side of the circuit and
probe sections of the circuit sequentially.
2. 
If the light is out or there is infinite resistance, the open is between the probe and the circuit ground.
3. 
If the light is...

Connect the multimeter negative lead to the batterys negative (-) post or terminal and the positive
lead to the batterys positive (+) post or terminal.
2. 
Turn the ignition switch ONto provide a load.
3. 
A well charged battery should register over 12 volts. If the meter reads below 11.5 volts, the battery
power may be insufficient to operate the electrical system properly.
4. 
VOLTAGE DROP
This voltage drop test revealed high resistance (low voltage) in the circuit
When current flows through a load,...