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Thread: Wiring diagrams

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    Senior Member DevonDavid's Avatar
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    Jan 2008
    East Devon
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    Wiring diagrams

    Prompted by the feeling that some owners feel a bit daunted by Jaguar wiring diagrams, may I offer the following.
    I apologise in advance to anyone who thinks I'm being too simplistic or patronising - just trying to help !!. Apart from the basic understanding that for any DC (direct current) bit of kit on a car to function, it needs both a 12 volt positive and a negative or ground connection to work, the rest has less to do with knowing about electronics, and more to do with solving a crossword puzzle or a Sudoku game. Compared with many other car manufacturers, Jaguar/Ford publish wiring diagrams in a very easy to understand format, and it isn't difficult to find your way around them.
    They are all available here : : a fantastic resource provided and maintained by an American guy called Gus Glikas - the Patron Saint of Jaguars.

    The first few pages are very useful in finding out where stuff is located - fuse boxes, earth points etc. Key information is wire colour codes (R = Red, Y = Yellow etc.) and also what the square and round symbols you will see later actually mean.
    A square box means a permanent 12 volt positive supply from the battery - always on.
    A circle means a 12 volt supply which is on when the ignition is on - a l in the circle means on at the first (auxiliary position), a ll means ignition on, and a lll means on "crank" position. An 'E' means that the power is supplied according to instructions from the engine computer.

    An octagonal shape means that the ground connection is determined by the position of the ignition switch, or by the ECM, rather than being a direct connection to the metalwork of the car. Other negative/ground connections are 4 small parallel lines forming the shape of an arrow. I'm not implying that Madbull doesn't know his way around the wiring diagram, but simply because it's a recent thread ............... ..... if we take the problem with headlamp washers.
    Figure 14.1 shows the whole Wash/Wipe system. The powerwash pump (top right) is permanently connected to ground by a brown wire. (right hand side). So - the 12v + feed must be from the YR (yellow & red) wire which comes from the powerwash relay. This has two square boxes, so permanent 12v positive supplies from somewhere called '5'. The ground supply comes from the Body Processor module with the YB wire. A relay is just a switch operated by an electric magnet. The switch part is at the top - after the switch there's a fuse - and the electric magnet is the rectangle below.
    The diagram also gives pin numbers for all connectors, and if you loook in the front section, there';s a detailed description of each connector (e.g. yellow 22 pin or black 6 pin) and also where to find it.

    So - zooming in a bit on that section, for the pump to work, there should be a permanent 12 volt positive supply on both pins 3 & 1 of the relay, and if you unplug the relay and bridge pins 3 & 5 the pump should work. If it does - the relay is at fault, or ......... there's a problem with the body processor module not supplying a negative feed to the relay when required. If it doesn't, the pump is faulty or the fuse has blown. The fuses are numbered, and the numbers - difficult to see - are etched into the plastic in the various fuse boxes.In either case, it is also possible that the ground / earth wire is not making proper contact, but that's easy to check with a test light or multimeter set to ohms or continuity.

    So - I hear you say - what about the 5s in the squares ? Well - if you look at figure/page 01.1, you will find the main power distribution diagram, and can see that the 12 volt positive starts with the battery, goes through two high power protection fuses (in the boot next to the battery) and then to the 5 fuse boxes in various parts of the car. 5 in a square is the engine compartment fuse box and you can see that one of the places that 12v goes to is figure/page 14.1 - the wash/wipe system page. (That's the six sort-of arrow rectangles which all indicate different figures / pages.)
    You can also see that the same 12 volt positive goes to both the coil and the switch of the "ignition positive" relay - the negative for the coil is from 10E (in the octagon) the ECM, - in other words - that relay is grounded by the ECM and when energised, supplies 12volts positive to 4ll when the ignition is on.

    If you were to go to figure/page 01.4, you can see that 4ll supplies power (12v +) to fuses 1 to 5 in the engine compartment fuse box, which then supplies fused 12v+ (when ignition is on) to various other places in the car.
    It really isn't about understading electrickery - just a case of detective work tracking a line, representing either a 12v+ or a negative/ground connection, from source to destination.

    Jaguar/Ford makes life just a little more complicated by changing various circuits and wire colours from one year to the next, so make sure you are looking at the correct diagram for your year/car, but otherwise, it is actually quite straightforward.
    Last edited by DevonDavid; 24-10-16 at 07:18.
    XK8 Convertible 4.0 - 1997. Aerial switch, boot lid switch, remote key-fob operated hood, & tensioners replaced.

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