manual radio set OPEL CALIBRA 1988 Service Repair Manual

1General information and
precautions
The electrical system is of 12-volt negative
earth type. Power for the lights and all
electrical accessories is supplied by a
lead/acid type battery, which is charged by
the alternator.
This Chapter covers repair and service
procedures for the various electrical
components not associated with engine.
Information on the battery, alternator and
starter motor can be found in Chapter 5.
It should be noted that, before working on
any component in the electrical system, the
battery negative terminal should first be
disconnected, to prevent the possibility of
electrical short-circuits and/or fires.
Whenever the occasion arises, carefully
check the routing of the wiring harness,
ensuring that it is correctly secured by the
clips or ties provided so that it cannot chafe
against other components. Carefully check
points such as the clutch cable bracket,
clutch housing and harness support bracket,
the inlet manifold, the horn mounting bracket,
the starter motor terminals, and the rear
bumper and number plate lamp.
If evidence is found of the harness having
chafed against other components, repair the
damage and ensure that the harness is
secured or protected so that the problem
cannot occur again.
2Electrical fault-finding -
general information
Note:Refer to the precautions given in “Safety
first!” (at the beginning of this manual) and to
Section 1 of this Chapter before starting work.
The following tests relate to testing of the main
electrical circuits, and should not be used to
test delicate electronic circuits (such as anti-
lock braking systems), particularly where an
electronic control module is used.
A typical electrical circuit consists of an
electrical component, any switches, relays,
motors, fuses, fusible links or circuit breakers
related to that component, and the wiring and
connectors that link the component to boththe battery and the chassis. To help to
pinpoint a problem in an electrical circuit,
wiring diagrams are included at the end of this
Chapter.
Before attempting to diagnose an electrical
fault, first study the appropriate wiring
diagram, to obtain a complete understanding
of the components included in the particular
circuit concerned. The possible sources of a
fault can be narrowed down by noting
whether other components related to the
circuit are operating properly. If several
components or circuits fail at one time, the
problem is likely to be related to a shared fuse
or earth connection.
Electrical problems usually stem from
simple causes, such as loose or corroded
connections, a faulty earth connection, a
blown fuse, a melted fusible link, or a faulty
relay (refer to Section 3 for details of testing
relays). Visually inspect the condition of all
fuses, wires and connections in a problem
circuit before testing the components. Use
the wiring diagrams to determine which
terminal connections will need to be checked,
to pinpoint the trouble-spot.
The basic tools required for electrical fault-
finding include the following:
a)a circuit tester or voltmeter (a 12-volt bulb
with a set of test leads can also be used
for certain tests).
b)a self-powered test light (sometimes
known as a continuity tester).
c)an ohmmeter (to measure resistance).
d)a battery.
e)a set of test leads.
f)a jumper wire, preferably with a circuit
breaker or fuse incorporated, which can
be used to bypass suspect wires or
electrical components.
Before attempting to locate a problem with
test instruments, use the wiring diagram to
determine where to make the connections.
To find the source of an intermittent wiring
fault (usually due to a poor or dirty
connection, or damaged wiring insulation), a
“wiggle” test can be performed on the wiring.
This involves wiggling the wiring by hand, to
see if the fault occurs as the wiring is moved.
It should be possible to narrow down the
source of the fault to a particular section of
wiring. This method of testing can be used in
conjunction with any of the tests described in
the following sub-Sections.
Apart from problems due to poor
connections, two basic types of fault can
occur in an electrical circuit - open-circuit, or
short-circuit.
Open-circuit faults are caused by a break
somewhere in the circuit, which prevents
current from flowing. An open-circuit fault will
prevent a component from working, but will
not cause the relevant circuit fuse to blow.
Short-circuit faults are caused by a “short”
somewhere in the circuit, which allows the
current flowing in the circuit to “escape” along
an alternative route, usually to earth. Short-
circuit faults are normally caused by abreakdown in wiring insulation, which allows a
feed wire to touch either another wire, or an
earthed component such as the bodyshell. A
short-circuit fault will normally cause the
relevant circuit fuse to blow.
Finding an open-circuit
To check for an open-circuit, connect one
lead of a circuit tester or voltmeter to either
the negative battery terminal or a known good
earth.
Connect the other lead to a connector in
the circuit being tested, preferably nearest to
the battery or fuse.
Switch on the circuit, remembering that
some circuits are live only when the ignition
switch is moved to a particular position.
If voltage is present (indicated either by the
tester bulb lighting or a voltmeter reading, as
applicable), this means that the section of the
circuit between the relevant connector and
the battery is problem-free.
Continue to check the remainder of the
circuit in the same fashion.
When a point is reached at which no
voltage is present, the problem must lie
between that point and the previous test point
with voltage. Most problems can be traced to
a broken, corroded or loose connection.
Finding a short-circuit
To check for a short-circuit, first disconnect
the load(s) from the circuit (loads are the
components that draw current from a circuit,
such as bulbs, motors, heating elements, etc.).
Remove the relevant fuse from the circuit,
and connect a circuit tester or voltmeter to the
fuse connections.
Switch on the circuit, remembering that
some circuits are live only when the ignition
switch is moved to a particular position.
If voltage is present (indicated either by the
tester bulb lighting or a voltmeter reading, as
applicable), this means that there is a short-
circuit.
If no voltage is present, but the fuse still
blows with the load(s) connected, this indicates
an internal fault in the load(s).
Finding an earth fault
The battery negative terminal is connected
to “earth” (the metal of the
engine/transmission and the car body), and
most systems are wired so that they only
receive a positive feed. The current returning
through the metal of the car body. This means
that the component mounting and the body
form part of that circuit. Loose or corroded
mountings can therefore cause a range of
electrical faults, ranging from total failure of a
circuit, to a puzzling partial fault. In particular,
lights may shine dimly (especially when
another circuit sharing the same earth point is
in operation). Motors (e.g. wiper motors or the
radiator cooling fan motor) may run slowly,
and the operation of one circuit may have an
affect on another. Note that on many vehicles,
earth straps are used between certain
components, such as the engine/transmission
and the body, usually where there is no metal-
12•2Body electrical systems
Warning: Before carrying out
any work on the electrical
system, read through the
precautions given in “Safety
first!” at the beginning of this manual, and
in Chapter 5.
Caution:If the radio/cassette player fitted
to the vehicle is one with an anti-theft
security code, as the standard unit is, refer
to “Radio/cassette player anti-theft system
- precaution”in the Reference Section of
this manual before disconnecting the
battery.