BMW 17 round pin radio connector introduced in 1991 to all BMW models.

BMW E36 radio wiring diagrams (without and with hi-fi amplifier)

Fader switch adjusts music balance between front and rear speakers. Most radios before 1991 had only 2 speaker channel outputs (L & R). With fader switch both signals are divided between front and rear speakers (LF, LR & RF, RR). With flat pins came at the beginning of the 80’s and with round pins (with smaller adjustment wheel) at the end of the 80’s. Only the later version has illumination. If installing any aftermarket head unit or my radio the fader switch should be bypassed + this feature is already built in the newer radios anyway.

For example BMW E32 fader switch delete – 4 outgoing speaker channels from the fader switch are now connected directly to the radios corresponding positive speaker outputs (pins 1, 2, 3, 6). Negative speaker outputs from the radio (8, 11, 12, 14) can be left disconnected and isolated as such old setups used common ground meaning the radios ground is the same as the speakers ground. Similar connecting principle can also be used with other BMW models that have fader switch, more examples below.

BMW E30 radio wiring diagrams, more info here

Radio adapters from old to new style (cars with fader switch have 2 channel audio wiring and this adapter is only compatible with round pin fader switch). Also antenna adapter is needed as E30, E28 and others before 1991 used older DIN standard connector instead of ISO.

BMW E24, E28, E30 and early E32 & E34 radio connectors until 1991

BMW E28 radio wiring diagrams

Aftermarket adapters for BMW