Wiring diagrams for motor vehicles

The following diagrams are reproduced by kind permission of the Ford Motor Company Ltd and show part of the wiring circuit for the Transit van. Service manuals need to be presented so that the technician can easily check each function for satisfactory operation. The manual is therefore written with each circuit shown completely and independently in one chapter or 'cell'. Other components which are connected to the circuit may not be shown unless they influence the circuit operation. For the benefit of the user, the diagram needs to be reasonably large to be used while work proceeds.

Figure 27.3 shows part of the circuitry for the headlamps. Each cell normally starts with the fuse, ignition switch, etc. that powers the circuit. Current flows from the power source at the top of the page towards earth at the bottom. Within the schematic diagram, all switches, sensors and relays are shown 'at rest' as if the ignition switch was in the OFF position. Page numbering system The Ford Motor Company procedure is to divide the electrical system into individual sections. For example, the Engine Control Section is 29. The section is further broken down into cells, where Cell 29.00 is the 2.OL2V engine, Cell 29.10 is the 2.OLEFI engine and so on. All the engine information can be found in cells 29.00 to 29.50. Finally the pages in the manual are numbered using the cell number, a dash, and then a consecutive number. If there are two pages in Cell 29.00, they will be numbered 29.00-00 and 29.00-01.

The headlamp circuit is continued at points 'A' & 'B' on to sheet number 32.00-02 down to the ground point G1001. The location of ground points is given on a separate diagram.

Connections to the Dim light relay, component K20, at the centre left side of diagram 32.00-01 are made via a connector, numbered C122. Connectors are grouped together on separate sheets and 91.00-05 (Fig. 27.5) is typical. The dim light relay connector is shown at the right centre side of this sheet. Looking at the connector, each wire is numbered to correspond with the circuit diagram, and recognizable by the colour coding.

Vehicle wiring is made up into looms and at the end of each of the bunches the connectors are fitted. Diagram 90.10-22 (Fig. 27.4) shows a pictorial view of wiring looms in the cab, and this is one of a series.

The circuits for Signal and Hazard indicators, also the Wiper/Washer control are given on diagrams 32.4000 and 32.60-01 (Fig. 27.3). Note that the switch N9 serves three functions. On 32.00-01 its function is to control Side/tail and Dipped beam on either side of the vehicle. On 32.60-01, the four wipe functions are actuated. Note also that on 32.40-00 the multi-function switch is illustrated in full. However four connections on this switch relate to headlamp functions so these details are given in full from points 8, 9, 10, 11 on 32.00-01. The location of connector C3 at position D1 on diagram 90.10-22 shows the connection to the Direction indicators at the top left corner on 32.40-00.

There are many pages similar to these in a vehicle service manual. This type of simplified layout has many advantages during servicing and fault finding operations.

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