ignition switch


  • ignition switch
  • Electrical part of ignition lock
  • Schematic of ignition switch with relief relay

Ignition switch:
The image below shows the back of an ignition lock. The ignition lock cylinder is located at the front and moves the electrical part of the ignition lock with the control element on the rear of the cylinder.
Because the electrical part (also called contact block) moves relative to the housing, various circuits are possible. The position of the key then indicates which contacts in the electrical part are connected to each other (e.g. when the constant positive wire (terminal 30) is connected to the positive wire of the starter motor (terminal 50b), starting. is released, terminal 15 (ignition) remains switched on. When the key is turned fully to the left again (to the off position), all contacts are broken and the engine and ignition are off).
When the key is removed from the ignition and the steering wheel is turned, the steering wheel lock is activated. An iron pin moves from the ignition switch into a notch in the steering column. To unlock the steering wheel lock again, turn the ignition key in the ignition lock while making a slight steering movement.

The operation of the lock cylinder is described on the page lock cylinder.

Nowadays, contact locks are increasingly used without a lock cylinder and work fully electronically by means of a plastic chip or key.

Electrical part of ignition lock:
Behind the lock cylinder is the electrical part, also called the "contact block". This actually ensures that the movement made with the key is converted to the tensions on the correct wires; so selecting the accessory mode and starting. 
The electrical part is often locked with a screw and is therefore fairly easy to remove from the housing of the ignition if a repair is needed.

The image on the right shows the front of the contact block. In the middle is a yellow, revolving part with a horizontal slot. When the key is inserted into the ignition, the end of the key will slide into this slot. When the correct key is inserted into the cylinder lock, it can turn thanks to the slats in the ignition lock. What you actually do is turn the yellow part in the contact block. Internally, the switch contacts (to which the plug is plugged at the back) are connected to each other. This is explained in more detail in the diagram in the next section.

It may happen that the car can no longer be started. In that case, the contact block may be internally defective. To check that, the control voltage on the small wire to the starter motor can be checked.
In older cars it was sometimes possible to remove the plug from the contact block and then connect certain contacts with its own wire. Or twist the yellow part with a screwdriver as you see in the image above. This allowed the car to be started and driven. Theft of cars often went this way.
To prevent this, an immobilizer is built into every car these days. The key number of the transponder in the key is compared with the stored values. If this does not match, the engine will stall immediately after starting. Nowadays it is therefore no longer possible to start and start the car with just the jumper of wires, or just operating the contact block.

See here more information about the immobilizer.

Schematic of ignition switch with relief relay:
The diagram below is of the ignition switch. This shows the component codes such as CS of the ignition and RX of the relief relay. The terminal codes 15, 30, 31, 50 and 75 are also shown here.

The moment the ignition lock is set to position 1, terminal 15 is connected to terminal 30. This means that the ignition is on and the consumers in the interior, among other things, are supplied with voltage. During cranking, terminal 50(b) is energized, causing the starter motor to rotate. When the ignition lock is turned to position 0 but the key is not yet withdrawn from the lock cylinder, voltage will remain on terminal 75. Terminal 75 contains consumers such as the radio. In the car of this scheme, the radio will therefore remain on if the ignition is off, and the key is not yet removed from the lock cylinder.

The function of the relief relay contact X (called “load reduction relay” in English) is to control consumers that require a lot of voltage and current to operate, such as the blower (interior fan), the radio, the dipped beam headlights, the rear window heating, the seat heating etc. when the engine is started. During starting, switch x in the ignition opens (as is the current situation in the schematic). The voltage to the solenoid (between terminals 85 and 86 of the control current side of the relay) is interrupted. As a result, no main current will flow via terminal 30 to 87, as a result of which the consumers, which are connected to wire number 102 in another scheme, are temporarily switched off. At that moment more power is available for the starter motor than when other consumers use a lot of power. Hence, this component is called a relief relay.
When the ignition key is turned back after the engine has started, the switch X in the ignition lock will close again. The relay RX is energized again, so that the consumers are supplied with voltage and current again.

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