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Stereo Upgrade

The stock stereo in my 528e served well for 11 years, but in 1997 I opted to install for a CD player, and wanted to improve on the stock speakers anyway (11 year old paper speakers get pretty dried out and frazzled in the heat of a car interior).   I settled on a Sony in-dash CD player/tuner, and 4 new Pioneer speakers, which I bought from Crutchfield (prices are probably better elsewhere, but their tech support was excellent).  I sold the stock stereo to a fellow BMW Digester for $50.

I bought new front speakers that fit right into the stock speaker locations in the footwell.  For the rear speakers I decided to install 6" speakers, even though the Crutchfield rep told me that they wouldn't fit.  I knew some cutting of the rear deck would be needed, but I figured it was worth it for the improved bass.  The cutting wasn't too difficult.  Be careful of the gas line and canister in the trunk near the right rear speaker! 

The only significant problem I encountered was that I could not simply use the stock speaker wiring, because the stock system uses a common ground (return) lead for front left and right speakers, and a second common lead for the rear left and right speakers, whereas the new unit demanded completely independent leads.  One solution is to run a complete set of new wiring from the new stereo to all four speaker positions.  An advantage to this approach is it allows you to install larger gauge wire.  However, I wasn't in the mood to completely rip apart the interior of my car, so I decided to re-use as much of the existing wiring as possible.  I dug into the wiring harness to find the splice point behind the fader control where the return leads from the left and right front speakers were spliced together.  I then simply spliced the front speaker leads for the new stereo to the existing speaker leads at that point.  However, even after much probing behind the instrument panel I was ultimately unable to find the splice point for the return leads from the left and right rear speakers, so I ended up running a new pair of speaker leads to the left rear speaker, and reused the existing leads for the right speaker.

528e Stereo Leads

When I replaced the stereo in my '86 E28 I noted the colors of all the leads.   These may also apply to '85s:

12 volt power, constant on


12 volt power, switched with ignition key


Antenna control lead (+12v when radio is on, otherwise ground)


Ground (battery return)


Headlights on (controls brightness of display)


Speaker: Left +


Speaker Left -


Speaker: Right +


Speaker: Right -



Following are the input and output color codes for the fader control.  The four speaker leads from the radio go to the fader control input; hence, the color codes for the fader inputs is identical to the color codes for the radio speaker outputs from the above table.  For the fader output there is a common return (-) lead for both front and rear speakers on each side.  If you replace the stereo with a modern unit and bypass the stock fader control you will probably have to run separate return (-) leads to each speaker position.

In: Left +


In: Left -


In: Right +


In: Right -


Out: Front Left +


Out: Rear Left +


Out:  Left - (common)


Out: Front Right +


Out: Rear Right +


Out:  Right - (common)



The power antenna has three leads: red for power (always on -- this powers the antenna motor so it can retract after you've turned off the ignition); white for the control lead that comes from the head unit (the head unit applies +12 volts to this lead when it wants the antenna to go up, and ground to go down); black for the ground lead.  Of course, there's also the black connectorized antenna cable.