What is the difference between a 3-position ignition switch and a 4-position ignition switch?

The difference between a 3-position ignition switch and a 4-position ignition switch is the number of different key positions and the functions associated with each position. These switches differ in the number of functions or circuits they control within the vehicle's electrical system.

As we can tell, both the three-position and four-position ignition switches are:

lOFF (0): in the off position, the vehicle's electrical system is completely shut down by removing or turning the key. No power is applied to the vehicle system.

lON: Turning the key to the ON position provides power to the vehicle's electrical system, including the instrument panel lights and other electronics, but does not start the engine.

lSTART: This position engages the starter motor and starts the engine.

Then the 4-position ignition switch will have an additional ACC switch, this position allows certain electrical accessories (such as the radio or interior lights) to operate without starting the engine, it provides power to vehicle accessories while keeping the engine turned off, allowing the user to operate certain electrical accessories without having to be in the full on position that powers all vehicle systems.

Or you may want to know how the ignition switch operates the car's circuits, and here's how it opens and closes.

①When the ignition switch is in the "OFF" position. When the key is turned to the "OFF" (off) position, the internal two contacts in the horizontal position are connected, that is, the external wires "black and white wire" and "green wire" are connected, so when the meter is used to measure the two wires at the "Ω" stop, the two wires should be in a state of conduction, while in the real car the two wires are connected. "Ω" block measurement of the two wires, should be on state, and in the real car in the two wires connected, said the car circuit system stops working, the ignition system circuit is in a short-circuit state, the engine is off.

② When the ignition switch in the "ON" position. Turn the key to "ON" (open) position, the horizontal position of the internal two contacts connected, that is, connected to the external wires "red wire" and "black wire", so that when using the meter "Ω" block measurement of the two wires, should also be on state, and in the actual car red, black two wires connected, said the signal system has been connected, the signal circuit is ready to work at any time.

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