ISO 10487 defines a standard for connectors for the head unit to the car's electrical system, consisting of a system of four different connectors typically used in head units for car audio.

ISO 10487 connector pinout (plug side of male, wiring side of female)

Power (A)

The first connector A is always present, is usually black in colour, and contains pins for power-supply, off/on (typically controlled by ignition key), optional control for a motorised antenna and so on.

On some cars the +12V Ignition and Battery positions are reversed, such as later Volkswagen group cars, Peugeot 106, Vauxhall Astra, Citroën C3.

Pin 1 is optional; used for speed dependent volume control and possibly navigation.

Pin 2 is optional; used for reversing lamp signal on Becker radios with navigation.

Pin 3 is also used for phone mute (Becker)

Pin 6 is optional; used for vehicle instrument illumination

Loudspeaker (B)

The second connector B is for connecting four loudspeakers, front, rear, left and right, and is usually brown in colour.

Miscellaneous (C)

The connector C is optional. Some times, it appears as one 20-pin connector, often red in colour, or it may be divided into three separate connectors which may be hooked together, in which case C1 is usually yellow, C2 is usually green which C3 is usually blue in colour. The contact spacing is narrower than the other connectors, so the C connector is sometimes referred to as mini-ISO.

Navigation (D)

The connector D is rarely used, and is for satellite navigation systems. It has 10 pins.