Hotwiring
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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. Hotwiring can also compromise the safety of the car, making it illegal to drive a hotwired car in some countries.
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[edit] 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.
The Accessory circuit, as can be seen in your vehicle's wiring diagrams, usually provides power to radios, cigarette lighters and interior lights. The ON circuit, in the case of a petrol 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 the starter motor.
To successfully hot-wire your vehicle the Accessory and ON circuits 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, 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.
Knowing which circuits are which, to non-destructively hot-wire the vehicle use a splicing crimp connector to bring wires for each circuit to a workable length. Using a switch or other method of electrical connection (twisting wires even) connect the always-live wire to the circuits for Accessory and On. At this point and if the instrument cluster is active, you may engage the starter motor circuit by momentarily connecting it to the 'always-powered' circuit. Turning off the vehicle is achieved by simply disconnecting the ON circuit from the voltage source.
Sometimes, it is possible to undertake these operations from within the engine compartment rather than from the dashboard, by making the same circuits as described above by direct links from the positive pole of the battery to the ignition and starter motor circuits.
Those who lack the necessary skills and knowledge of electrical engineering to hotwire a car in the classical way sometimes use a brute-force method: simply smashing the key mechanism to reveal the rotation switch, which is operated by the key's tumbler. In a criminal context, this could be accomplished with the same tool that may have been used to smash the vehicle's windows to gain entry. The rotary switch can then be operated by a screwdriver or similar tool.
[edit] Countermeasure Technologies
Some more modern vehicles are designed to overcome the relative ease with which classical ignition systems can be hotwired. This is primarily accomplished through the use of engine immobiliser devices which disable the engine in some manner. Such systems require a code key to disengage. The code key could be analog (such as the precise resistance of the physical key) or digital (such as a passcode embedded in a USB or similar electronic key). As automobile electronics advance, hotwiring is expected to become increasingly difficult. However, these immobilization devices are themselves now subject to hot-wiring.
There are ways to bypass these safety mechanisms; since most engine immobilisers are actually implemented in a subroutine of the electronic engine control unit, in the process of stealing a car some criminals simply replace said control unit with a reprogrammed one which they brought along with them. This method of hotwiring is typically carried out on more expensive automobiles and by thieves scouting for a specific model. Some automakers have responded to this problem by making it increasingly difficult to remove the unit from a car, either by riveting it to the body or by thoroughly shrink-wrapping it and the wires connected to it.
[edit] Other
It is possible that the increased difficulty of hotwiring has led to the rise in carjacking in other ways, such as stealing car keys.[citation needed] However, security and insurance experts agree that most auto thefts can be deterred by employing common sense safety methods, such as never leaving spare keys in plain sight (or keeping spare keys inside the vehicle).
