One of the less obvious places to look for starting problems or the engine cutting out while driving is the drum behind the ignition switch. Over time the contacts in the drum will get dirty or water leaking from round the windscreen may find its way into the drum and corrode the contacts.

The three wires on the back of the drum are as follows:-
Black sleeve - permanently live, feed to ignition switch from battery
Mauve sleeve (may appear white) - live when ignition switch is in 'on' position, feeding fuel gauge, coil, wipers, indicators and all other equipment which only works with the ignition on.
Red sleeve - live when ignition key is in 'start' position, sends power to starter motor.

There are three scenarios where poor contacts in the drum may be the cause of the problem.
1) You turn the ignition on but the oil pressure light, fuel gauge, wipers, and all items which only work with the ignition on, are not working.
2) You try to start the engine but the starter motor is 'dead' but all the items in 1 above are working.
3) Your engine suddenly cuts out while driving. If, at the same time, the fuel gauge suddenly goes to 'Empty' or other items which only work with the ignition on suddenly stop working, the drum could well be the cause.

You may be able to overcome problems by turning the ignition on and off a few times which might clear dirt or corrosion. If that fails you need to remove the drum. Disconnect the 3 wires (remembering which way they have to go back!). Lift the circlip sufficiently to free the drum (photos below) and pull it away from the switch. Use a switch cleaner aerosol down the inside of the drum around the sides of the rotating (white plastic) inner component. Refit the unit to the back of the switch ensuring the pin from the switch fits in the slot of the inner component of the drum and locate the circlip. Replace the 3 wires on the correct terminals ensuring they are a tight fit. If that fails to cure the problem we suggest a new drum.

We don't recommend removing the inner component of the drum to clean the contacts manually but this is how it works. It consists of two concentric circular plastic mouldings which can rotate independently of eachother. The upper part is turned by the pin from the ignition key which fits into the slot (see photo). This upper part runs in a sort of thread on the inside of the drum so when turned clockwise by the key it descends into the drum in the same way as a screw would. The lower part which carries two pairs of electrical contacts cannot turn as it has pegs between each pair of contacts which locate in slots cut through the side of the drum (see photo). So the lower part descends vertically in the drum as the upper part is turned. As the entire inner component descends into the drum, one pair of contacts connects to a pair of contacts on the inside wall of the drum and this turns the ignition on. As the key is turned further the second pair of contacts connect to another pair on the inside of the drum and operate the starter.

The component can be removed from the drum by simply prising it out but refitting it is very fiddly. Getting the pegs to locate in the slots in the drum is difficult and they are likely to break if you use too much force.
The photo on the right shows the inner component's peg in the slot in the side of the drum. NB The circlip has been slid down from its groove just far enough to be able to remove the drum from the switch.
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