Several types of connectors for car audio systems is used.
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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.
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), optionally control for a motorised antenna and so on. Pinout viewed from the cable side of the female connector:
| clip | 1) speed signal [2] | 3) N/C [4] | 5) remote antenna (out) | 7) +12 V switched [1] |
| 2) phone mute [3] | 4) +12 V battery [1] | 6) illumination [5] | 8) ground |
[1] On some cars the +12V Ignition and Battery positions are reversed, such as later Volkswagen group cars, Peugeot 106, Vauxhall Astra, Citroën C3.
[2] Optional, used for speed dependent volume control and possibly navigation.
[3] Optional. Used for reversing lamp signal on Becker radios with navigation.
[4] Also used for phone mute (Becker)
[5] Optional, vehicle instrument illumination
The second connector B is for connecting loudspeakers, and is usually brown in colour. Pinout viewed from the cable side of the female connector:
| clip | 1) right rear (+) | 3) right front (+) | 5) left front (+) | 7) left rear (+) |
| 2) right rear (−) | 4) right front (−) | 6) left front (−) | 8) left rear (−) |
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.
| 1) line out left rear | 4) line out left front | |||
| 3) line out common ground | 6) +12V switched (out) | |||
| 2) line out right rear | 5) line out right front | |||
| 7) receive data | 10) +12V switched (out) | |||
| 9) chassis ground | 12) remote control ground | |||
| 8) transmit data | 11) remote control in | |||
| 13) data in (bus) | 16) +12v switched (out) | 19) audio left | |||
| 15) +12v permanent (out) | 18) audio ground | ||||
| 14) data out | 17) data ground | 20) audio right | |||
The connector D is rarely used, and is for satellite navigation systems. It has 10 pins.
From 2000 and onwards, manufacturers, such as BMW, Citroen, Ford, Mercedes Benz, Peugeot, Volkswagen, Rover, Audi, Seat, Opel and Skoda have started using a 40 pin connector instead, called the Quadlock (or Fakra, after the manufacturer). The Quadlock connector consists of a block of 16 flat pins analogous to the two main ISO 10487 connectors. While the physical contact pins are the same, the pin allocation is not entirely the same, and the connector housing is not compatible. In addition to the 16 pins, like ISO 10487, there are minor connectors for optional equipment. They fit within the frame of the main connector, and has coding so that they cannot be interchanged. Minor connector B has 12 pins for audio output signals. Minor connector C has 12 pins for various audio sources such as CD-changers, MP3 players.
| 1) right rear + | 5) right rear - | 9) I-bus (BMW) | 13) antenna (out) | |
| 2) right front + | 6) right front - | 10) phone mute | 14) illumination | |
| 3) left front + | 7) left front - | 11) tel on | 15) 12V battery | |
| 4) left rear + | 8) left rear - | 12) ground | 16) 12V switched |