How do you start a car with a bad ignition?

Answer 1

It depends largely on what vehicle, what transmission, and what, exactly the ignition malfunction is. If the ignition switch malfunctions in such a way that the 'On' position doesn't function, there's really not much you can do besides replacing the switch and starting the engine as normal; Not a very common situation, but it can happen.

For vehicles with automatic transmissions, you're pretty much stuck with one option (besides fixing the switch); You have to physically make the connection between two of the electrical terminals on the starter solenoid by either installing your own switch, or using a screwdriver (or similar object) to jump the terminals until the engine starts (Don't forget, the ignition must be in the 'ON' position, or the engine still won't start). It should go without saying that this presents something of a safety risk, so if you don't know what you're doing, don't do it, or have someone who knows how show you.

For vehicles with manual transmissions, you have the above option, plus the vehicle can be push started. Just turn the ignition on, put the transmission in 2nd or 3rd gear with the clutch pedal pressed to the floor, get the vehicle moving (hopefully you're on a hill or you have strong friends or a tow/pushing vehicle), then 'pop' the clutch up for a second to let the vehicle motion turn the engine over, but press the clutch back to the floor quickly before the engine stalls from mismatched engine/transmission/road speeds. It may take more than one attempt to get it right, and please be careful while attempting this.