The ignition switch in your car is very important and has many uses. To start with, it helps you control the supply of power to various parts of the car, so that they do not keep running for a long time and use up all the car battery when it is parked or not running. However, it is most crucial function is to connect the car battery and the starter, so that when you turn the switch 'on', electricity is passed on to the starter which starts the engine, thereby starting your vehicle.
The ignition switch relay or the starter relay, is a device which helps in regulating the huge amount of current required to start the car, with help of a small amount of current. This is essential because you cannot pass a large amount of current through the switch. In case you wanted to, you would require a large-sized ignition switch along with wires of the size of battery cables, which is practically impossible.
Ignition switch as a term, refers to two different parts - the lock cylinder where you stick in you car key, and the electronic switch right behind the cylinder. Depending on the type of car you have, these may be either combined into a single unit or remain separate. It is therefore important to check this in your car manual before you buy a new assembly, for the removal and replacement process.
Any one of the two parts could fail, prompting you to remove and replace the ignition switch. The symptoms, however, for each of these are different. An ignition switch failure can be the cause of - the car not starting, the spring-loaded 'on' position not functioning or problems in the electrical wiring. While, signs like - lock cylinder not turning, key coming out even when car is moving, any key starting your car or any other malfunctioning of the keys, indicate a problem with the lock cylinder.
Replacing an Ignition Switch
Unscrew and remove both the upper, as well as lower steering column covers. The negative battery cable should also be pulled out from the battery terminal.
You will then have to take out the steering wheel. Do this by raising the center cover, unplugging the horn wire and taking out the retaining washer and nut. Once you have done this, hold the steering wheel tight and pull it hard towards you to remove it out from the shaft.
Unplug all wires of the signal switches and pull them out. Also remove the windshield wiper and glide the spacer sleeve away from the steering column.
Your ignition switch will have mounting screws. Unscrew them and draw out the switch. Also unplug the wiring connector present behind the switch, loosen its tabs, and take it out.
You will then have to turn the ignition switch to the 'locked' position, by inserting your car keys into the ignition switch. Use a small screwdriver to lower the retaining pin and then turn the car key to the 'off' position. This will free the ignition cylinder. After this, again turn the key to the 'lock' position and take out the keys as well as the cylinder.
The key cylinder you removed will go into the new ignition switch assembly. Join all wires properly in the new assembly by referring to the manual. This new assembly will have to be slid into the designated slot. Now simply screw back the mounting screws and put back the steering wheel and switches.
Before you start this endeavor, you should understand the fact that this process differs from car to car, depending on the manufacturer. Go through the manual thoroughly to understand your car mechanisms, so that you can successfully remove and replace the ignition switch. In case you are not comfortable in doing it yourself, you can always take help from a motor mechanic who specializes in such repair.