Ignition Wires

Hotwiring is the process of bypassing an automobile's ignition interlock and thus starting it without the key. Although it is not illegal if performed with the consent of the car owner, the activity is usually performed by criminals who intend to steal the vehicle. more...

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Hotwiring can also compromise the safety of the car, making it illegal to drive a hotwired car in some countries.

Method

To know how to hot-wire a vehicle it is important to first understand how a vehicle's electrical system works. In most petrol or diesel powered vehicles there are a number of positions the key can turn to, such as Lock/Off, Accessory, ON and Start. Each of these positions activates a corresponding electrical circuit in the vehicle - in other words it is a multiple position switch, with only one power entry line (one input for 4 outputs).

The Accessory circuit, as can be seen in your vehicle's wiring diagrams, usually provides power to radios and cigarette lighters. The ON circuit, in the case of a gasoline vehicle, provides power to the ignition coil(s), enables the instrument cluster and fuel injection/spark control computer. The Start circuit is nearly always a circuit to a relay which engages and activates the starter motor.

Older vehicles, namely ones from pre mid 80's, which have a carbureted engine and a single ignition coil and distributor, can be hotwired from the engine bay. A small lead with alligator clips on both ends (or ring terminals for more advanced and reliable thefts) sometimes along with an inline switch, is connected between the positive terminal of the battery and the positive terminal of the ignition coil. This simulates the ON position of the key switch and energises the ignition system. Another small jumper lead is used to connect the positive terminal of the battery to the solenoid terminal on the starter motor, and usually has a momentary push-switch inline to act as a starter switch. This activates the starter motor (simulates the START position of the key switch) and providing there is ignition power, the engine will start. But entry to the car must still be gained and the steering lock broken.

To successfully hot-wire your vehicle at least the ON circuit(s) must be enabled prior to powering the starter motor circuit. This resembles the normal operation of your key-start where circuits are incrementally enabled relative to key position and with the starter motor being only momentarily enabled. Once you have gained permitted access to the rear of the vehicle's key-start mechanism you will need to determine which wire is connected to each circuit. Using a multi-meter (or test light or similar), check for a voltage on one wire relative to the vehicle's electrical ground as you turn the key to a certain position ie, when you turn the key to Accessory voltage should appear on one wire and disappear when turned back off. There should be one wire with voltage on it even when off, this power source is switched onto the other circuits by the key-start. You can repeat this process with all the key-positions you need to emulate until you understand which circuits you need to manipulate.

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