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Types of Positive Cables in Cars

Model: (Various brands) Various
Part: Checks and maintenance

Video tutorial

There are different types of positive cables in a car: those that are always live (even with the engine off) that power devices that must always function, such as courtesy lights, radio memory, central locking module, and hazard lights. Then there are those known as 'switched live', which are active only with the ignition on, and temporarily deactivate during starting to avoid current spikes, such as the radio, windscreen wipers, interior lights, and on some models, even the radiator fan. There are also 'engine live' cables, which are managed by the control unit, active only with the ignition on but do not turn off during starting.

They power critical engine components, such as injectors, coils, sensors, and solenoids. Then there is the positive for warning lights and dashboard, which is similar to the switched live but does not turn off during starting.

It is important to know this difference to avoid short circuits or damage to components and to prevent draining the battery (for example, with the radio always powered). To connect devices to the correct cable, how do you identify a switched live cable? With a multimeter: with the ignition off, voltage is 0V; with the ignition on, voltage is 12V. During starting, the voltage drops to 0, then reactivates.


Posted on 2 April 2026 by ScegliAuto


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