Chapter 1 Routine maintenance and servicing

1595Ford Fiesta Remake12•4 Body electrical systemswiring diagrams are included at the end of thismanual.2 Before attempting to diagnose an electricalfault, first study the appropriate wiringdiagram, to obtain a complete understandingof the components included in the particularcircuit concerned. The possible sources of afault can be narrowed down by noting if othercomponents related to the circuit areoperating properly. If several components orcircuits fail at one time, the problem is likely tobe related to a shared fuse or earthconnection.3 Electrical problems usually stem fromsimple causes, such as loose or corrodedconnections, a faulty earth connection, ablown fuse, a melted fusible link, or a faultyrelay (refer to Section 3 for details of testingrelays). Visually inspect the condition of allfuses, wires and connections in a problemcircuit before testing the components. Usethe wiring diagrams to determine whichterminal connections will need to be checkedin order to pinpoint the trouble-spot.4 The basic tools required for electrical faultfindinginclude a circuit tester or voltmeter (a12-volt bulb with a set of test leads can alsobe used for certain tests); an ohmmeter (tomeasure resistance and check for continuity);a battery and set of test leads; and a jumperwire, preferably with a circuit breaker or fuseincorporated, which can be used to bypasssuspect wires or electrical components.Before attempting to locate a problem withtest instruments, use the wiring diagram todetermine where to make the connections.Warning: Under nocircumstances may livemeasuring instruments such asohmmeters, voltmeters or a bulband test leads be used to test any of theair bag circuitry or components. Anytesting in these areas must be left to aFord dealer as there is a danger ofactivating the system if the correctprocedures are not followed.5 To find the source of an intermittent wiringfault (usually due to a poor or dirtyconnection, or damaged wiring insulation), a“wiggle” test can be performed on the wiring.This involves wiggling the wiring by hand tosee if the fault occurs as the wiring is moved.It should be possible to narrow down thesource of the fault to a particular section ofwiring. This method of testing can be used inconjunction with any of the tests described inthe following sub-Sections.6 Apart from problems due to poorconnections, two basic types of fault canoccur in an electrical circuit - open-circuit, orshort-circuit.7 Open-circuit faults are caused by a breaksomewhere in the circuit, which preventscurrent from flowing. An open-circuit fault willprevent a component from working.8 Short-circuit faults are caused by a “short”somewhere in the circuit, which allows thecurrent flowing in the circuit to “escape” alongan alternative route, usually to earth. Shortcircuitfaults are normally caused by abreakdown in wiring insulation, which allows afeed wire to touch either another wire, or anearthed component such as the bodyshell. Ashort-circuit fault will normally cause therelevant circuit fuse to blow.Finding an open-circuit9 To check for an open-circuit, connect onelead of a circuit tester or the negative lead of avoltmeter either to the battery negativeterminal or to a known good earth.10 Connect the other lead to a connector inthe circuit being tested, preferably nearest tothe battery or fuse. At this point, batteryvoltage should be present, unless the leadfrom the battery or the fuse itself is faulty(bearing in mind that some circuits are liveonly when the ignition switch is moved to aparticular position).11 Switch on the circuit, then connect thetester lead to the connector nearest the circuitswitch on the component side.12 If voltage is present (indicated either bythe tester bulb lighting or a voltmeter reading,as applicable), this means that the section ofthe circuit between the relevant connectorand the switch is problem-free.13 Continue to check the remainder of thecircuit in the same fashion.14 When a point is reached at which novoltage is present, the problem must liebetween that point and the previous test pointwith voltage. Most problems can be traced toa broken, corroded or loose connection.Finding a short-circuit15 To check for a short-circuit, firstdisconnect the load(s) from the circuit (loadsare the components which draw current froma circuit, such as bulbs, motors, heatingelements, etc).16 Remove the relevant fuse from the circuit,and connect a circuit tester or voltmeter to thefuse connections.17 Switch on the circuit, bearing in mind thatsome circuits are live only when the ignitionswitch is moved to a particular position.18 If voltage is present (indicated either bythe tester bulb lighting or a voltmeter reading,as applicable), this means that there is ashort-circuit.19 If no voltage is present during this test,but the fuse still blows with the load(s)reconnected, this indicates an internal fault inthe load(s).Finding an earth fault20 The battery negative terminal isconnected to “earth” - the metal of theengine/transmission and the vehicle body -and many systems are wired so that they onlyreceive a positive feed, the current returningvia the metal of the car body. This means thatthe component mounting and the body formpart of that circuit. Loose or corrodedmountings can therefore cause a range ofelectrical faults, ranging from total failure of acircuit, to a puzzling partial failure. Inparticular, lights may shine dimly (especiallywhen another circuit sharing the same earthpoint is in operation), motors (eg wipermotors or the radiator cooling fan motor) mayrun slowly, and the operation of one circuitmay have an apparently-unrelated effect onanother. Note that on many vehicles, earthstraps are used between certaincomponents, such as the engine/transmission and the body, usually wherethere is no metal-to-metal contact betweencomponents, due to flexible rubbermountings, etc.21 To check whether a component isproperly earthed, disconnect the battery (referto Chapter 5A, Section 1) and connect onelead of an ohmmeter to a known good earthpoint. Connect the other lead to the wire orearth connection being tested. The resistancereading should be zero; if not, check theconnection as follows.22 If an earth connection is thought to befaulty, dismantle the connection, and cleanboth the bodyshell and the wire terminal (orthe component earth connection matingsurface) back to bare metal. Be careful toremove all traces of dirt and corrosion, thenuse a knife to trim away any paint, so that aclean metal-to-metal joint is made. Onreassembly, tighten the joint fastenerssecurely; if a wire terminal is being refitted,use serrated washers between the terminaland the bodyshell, to ensure a clean andsecure connection. When the connection isremade, prevent the onset of corrosion in thefuture by applying a coat of petroleum jelly orsilicone-based grease, or by spraying on (atregular intervals) a proprietary ignition sealeror a water-dispersant lubricant.3 Fuses and relays -general informationNote: It is important to note that the ignitionswitch and the appropriate electrical circuitmust always be switched off before any of thefuses (or relays) are removed and renewed.1 The main fuse and relay board is locatedbelow the facia panel to the right of thesteering wheel. The fuses can be inspectedand if necessary renewed, by removing thehinged access cover. The remainingadditional fuses and relays (depending onmodel) may be accessed by removing the twofuse board retaining screws, releasing theretaining lugs on either side of the main fuseplate and withdrawing the fuse/relay boarddownwards into the driver’s footwell. Eachfuse location is numbered - refer to the fusechart in the Specifications at the start of thisChapter to check which circuits are protectedby each fuse. Plastic tweezers are attached to