Electrical Troubleshooting-General Information; Fuses-General Information - Jeep cherokee 1989 Owner's Manual

2 Electrical troubleshooting
A typical electrical circuit consists of an electrical component, any
switches, relays, motors, fuses, fusible links or circuit breakers related
t o that component and the wiring and connectors that link the com-
ponent to both the battery and the chassis. To help you pinpoint an
electrical circuit problem, wiring diagrams are included at the end of
this book.
Before tackling any troublesome electrical circuit, first study the ap-
propriate wiring diagrams t o get a complete understanding of what
makes up that individual circuit. Trouble spots, for instance, can often
be narrowed down by noting if other components related to the circuit
are operating properly. If several components or circuits fail at one time,
chances are the problem is in a fuse or ground connection, because
several circuits are often routed through the same fuse and ground
connections.
Electrical problems usually stem from simple causes, such as loose
or corroded connections, a blown fuse, a melted fusible link or a bad
relay. Visually inspect the condition of all fuses, wires and connec-
tions in a problem circuit before troubleshooting it.
If testing instruments are going t o be utilized, use the diagrams to
plan ahead of time where you will make the necessary connections
in order t o accurately pinpoint the trouble spot.
The basic tools needed for electrical troubleshooting include a circuit
tester or voltmeter (a 12-volt bulb with a set of test leads can also
be used), a continuity tester, which includes a bulb, battery and set
of test leads, and a jumper wire, preferably with a circuit breaker in-
corporated, which can be used to bypass electrical components. Before
attempting t o locate a problem with test instruments, use the wiring
Voltage checks
Voltage checks should be performed if a circuit is not functioning
properly. Connect one lead of a circuit tester t o either the negative
battery terminal or a known good ground. Connect the other lead t o
a connector in the circuit being tested, preferably nearest t o the battery
or fuse. If the bulb of the tester lights, voltage is present, which means
that the part of the circuit between the connector and the battery is
problem free. Continue checking the rest of the circuit in the same
fashion. When you reach a point at which no voltage is present, the
problem lies between that point and the last test point with voltage.
Most of the time the problem can be traced to a loose connection. Note:
Keep in mind that some circuits receive voltage only when the ignition
key is in the Accessory or Run position.
Finding a short
One method of finding shorts in a circuit is to remove the fuse and
connect a test light or voltmeter in its place to the fuse terminals. There
should be no voltage present in the circuit. Move the wiring harness
from side-to-side while watching the test light. If the bulb goes on,
there is a short to ground somewhere in that area, probably where the
insulation has rubbed through. The same test can be performed on each
component in the circuit, even a switch.
Ground check
Perform a ground test to check whether a component is properly
grounded. Disconnect the battery and connect one lead of a self-
powered test light, known as a continuity tester, to a known good
ground. Connect the other lead to the wire or ground connection being
tested. If the bulb goes on, the ground is good. If the bulb does not
go on, the ground is not good.
Continuity check
A continuity check is done t o determine if there are any breaks in
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a circuit if it is passing electricity properly. With the circuit off (no
power in the circuit), a self-powered continuity tester can be used to
check the circuit. Connect the test leads to both ends of the circuit
(or to the "power" end and a good ground), and if the test light comes
on the circuit is passing current properly. If the light doesn't come on,
there is a break somewhere in the circuit. The same procedure can
be used t o test a switch, by connecting the continuity tester t o the
switch terminals. With the switch turned On, the test light should come
on.
The Motor Manual Guy
Chapter 12 Chassis electrical system
general information
Finding an open circuit
When diagnosing for possible open circuits,
locate them by sight because oxidation or terminal misalignment are
hidden by the connectors. Merely wiggling a connector on a sensor
or in the wiring harness may correct the open circuit condition.
Remember this when an open circuit is indicated when troubleshooting
a circuit. Intermittent problems may also be caused by oxidized or loose
connections.
Electrical troubleshooting is simple if you keep in mind that all elec-
trical circuits are basically electricity running from the battery, through
the wires, switches, relays, fuses and fusible links t o each electrical
component (light bulb, motor, etc.) and to ground, from which it is
passed back t o the battery. Any electrical problem is an interruption
in the flow of electricity to and from the battery.
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3 Fuses general information
3.3
Refer to illustrations 3. 1 and
The electrical circuits of the vehicle are protected by a combination
of fuses, circuit breakers and fusible links. The fuse block is located
under the instrument panel on the left side of the dashboard (see
illustration).
Each of the fuses is designed to protect a specific circuit, and the
various circuits are identified on the fuse panel itself.
Miniaturized fuses are employed in the fuse block. These compact
fuses, with blade terminal design, allow fingertip removal and replace-
ment. If an electrical component fails, always check the fuse first. A
blown fuse is easily identified through the clear plastic body. Visually
inspect the element for evidence of damage (see illustration). If a con-
tinuity check is called for, the blade terminal tips are exposed in the
fuse body.
Be sure t o replace blown fuses with the correct type. Fuses of dif-
ferent ratings are physically interchangeable, but only fuses of the pro-
per rating should be used. Replacing a fuse with one of a higher or
lower value than specified is not recommended. Each electrical circuit
The fuse block is located under the left side of the
3.1
instrument panel
3.3
To check for a blown fuse, pull it out and inspect it
visually for an open (I), then with the circuit activated. use
a test light across the points shown
12-1
it is often difficult t o
HAZARD
FLASHER