Radio Connector/Harness Differences

[radlaw]

There are differences between the car radio connector pins and the radio harness:
1) Different number of pins: 15 slots in the car connector & 13 pins in the harness. What is missing in the harness?
2) There's a white connector in the car connector (lower left) and nothing matching in the harness.

3) Does anyone know what the individual car connector slots are for?

car radio connector.jpg Car connector
radio harness.jpg Harness

[Timm]

Here you go:

http://www.meeknet.co.uk/e31/becker/...nit_Pinout.jpg

[revtor]

There are differences between the car radio connector pins and the radio harness:
1) Different number of pins: 15 slots in the car connector & 13 pins in the harness. What is missing in the harness?

For the pin layout see Timm's picture. Here are the English translations:

1 Front left speaker +
2 Front right speaker +
3 Rear left speaker +
4 Telephone mute
5 Switched +12V
6 Rear right speaker +
7 n/a (*1)
8 Front left speaker -
9 Permanent +12V
10 GAL speed signal
11 Front right speaker -
12 Rear left speaker -
13 Illumination
14 Rear right speaker -
15 Ground
16 Remote power for antenna and audio amplifier
17 n/a (*2)

(*1) Pin 7 is the I-bus. While the E31 technically has the I-bus (in fact it was the first BMW vehicle to be equipped with it) it was implemented at a small scale and is slightly different from the I-bus in later BMW models. In later BMW models the I-bus connection is used for radio control via multifunction steering wheel buttons and car phone integration. This was never available for the E31 and hence the radio harness is not connected to the I-bus.

(*2) Pin 17 is always unused. It may have been reserved for future functionality but that never materialized and BMW later changed to a different connector.

2) There's a white connector in the car connector (lower left) and nothing matching in the harness.

Cable to the CD changer in the trunk / luggage compartment.

[radlaw]

Thanks to you both. I got it all except #10 GAL speed signal. Out of curiosity, what is that?

[revtor]

The speed signal is used for speed-dependent volume control (GAL). The faster you drive the louder the head unit will go to compensate for the road/wind noise.

Some head units with navigation (aftermarket for the E31 like the Becker Indianapolis) also use the signal for (linear) position tracking when no GPS reception is available (ie tunnel).