12*2 Body electrical systems
3 Electrical problems usually stem from simple causes, such as loose or corroded connections, a faulty earth connection, a blown fuse, a melted lusible link, or a fautty relay {refer to Section 3 for details of testing relays). Visually inspect the condition of all (uses, wires and connections in a problem circuit before testing the components. Use the wiring diagrams lo determine which terminal connections will need to be checked, in order to pinpoint the trouble-spot. 4 The basic tools required for electrical fault-finding include a circuit tester or voltmeter (a 12-volt bulb with a set of lest leads can also be used for certain tests}; a self-powered test light (sometimes known as a continuity tester); an ohmmeter (to measure resistance): a battery and set of tesi leads: and a lumper wire, preferably with u circuit breaker or fuse incorporated, which can be used to bypass susoect wires or electrical components. Before attempting to locate a problem with tost instruments, use the wiring diagram to determine where to make the connections. 5 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 tha 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 descnbed in the following sub-Sections. 6 Apart from problems due to poor connections, two basic types of fault can occur in an electrical circuit - open-circuit, or short-circuit. 7 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 8 Short-circuit faults are caused by a shod somewhere in the circuit, which allows Die current flowing In the circuit to escape along an alternative route, usually to earth. Short-circuit faults are normally caused by a breakdown in wiring insulation, which allows a feed wire to touch either another wire, or an earthed component such as the bodysheli. A short-circuit fault will normally cause the relevant circuit fuse to blow.
Finding an open-circuit 9 To check for an opon-circuit, connect one lead of a circuit tester or voltmoter to either the negative battery terminal or a known good earth. 10 Connect the other lead to a connector in the circuit being tested, preferably nearest to the batter/ or luse. 11 Switch on the circuit, bearing In mind that some circuits are live only when tho ignition switch is moved to a particular position. 12 If voltage is present (Indicated either by
3.2 Main fuse box, located on the driver's side of the facie the toster bulb lighting or a voltmeter reading, as applicable), this means that tho section of Ihe circuit between the relevant connector and the battery is problem-free. 13 Continue to check the remainder ot the circuit in the same fashion. 14 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 15 To check for a short-circuit, first disconnect the load(s) from the circuit (loads are the components which draw current from a circuit, such as bulbs, motors, heating elements, etc). 16 Remove the relevant luse Irom the circuit, and connect a circuit tester or voltmeter to the luse connections. 17 Switch on the circuit, beanng in mind that some circuits are live only when the ignition switch is moved to a particular position. 18 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. 19 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 20 The battery negative terminal Is connected to 'earth' - the metal of the engine/transmission and the car body - and
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J 3.3 To gain access to the fuses, remove the screw and pull the stowage bin away from the facia
most systems are wired so that they only receive a positive feed, the current returning via the metal of Ihe 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 ot a circuit, to a puzzling partial fault. In particular, lights may shine dimly (especially when another circuit sharing the same earth port In operation), motors (eg wiper motors v Ihe radiator cooling fan motor) may run slowly, and Ihe operation of one circuit may have an apparently-unrelated effect on another. Ncie that on many vehicles, earth straps axe uses between certain components, such as the engine/transmission and the body, usually whore there is no metal-to-metal contact between components, due to flexible rubber mountings, etc. 21 To check whether a component $ properly earthed, disconnect Ihe battery, and connect one lead of an ohmmeter to a kwwi good earth point. Connect the other lead to the wire or earth connection being tested. Tha resistance reading should be zero; if not. check the connection as follows. 22 If an earth connection Is thought to be faulty, dismantle the connection, and clean pack to bare metal both the bodysheli and ite wire terminal or the component earth connection mating surface. Be careful to remove all traces of dirt and corrosion, then use a knife to trim away any palm, so thai a clean metal-to-metal joint Is mads. On reassemoly, tighten the joint fasteners securely: if a wire terminal Is being refitted, use serrated washers between tho terminal and the bodysheli. to ensure a clean and secure connection. When the connection is remade, prevent the onset ot corrosion in the future by applying a coat of petroleum idly
or
stlicone-based grease, or by spraying on (a: regular intervals} a proprietary ignition eoater, or a water-aispersant lubneant.
3 Fuses and relays -general information
Fuses 1 Fuses are designod to break a circuit when a predetermined current is reached, in order to protect the components and wiring wttioh could be damaged by excessive current How. Any excessive current flow will be due to a fault in the circuit, usually a short-circuit (see Section 2). 2 The main fuses are located in the fusefcox on the driver's side of the facia (see illustration). 3 To gain access to the fuses, remove tne screw and pull the stowage bin moulding away from the facia (see illustration). 4 Additional fuses and circuit-breakers are located In the engine compartment, and in an
