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Old 04-28-2019, 03:48 PM   #1
bradnic
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Join Date: Jul 2012
Location: Chicago
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Understanding E30 speaker and amp wiring

Posted this to Luke's wiring thread, but think it warrants it's own post. Should probably sticky this too.

Radios like the CM5908 and KE83ZBM have 4 amp channels (and a CD changer connector). the earlier radios like the CM5905, CM5907 and KE81ZBM only have 2 amp channels. If you have the 4 channel setup with the BMW Sound System (tweeters on all four corners for coupes and sedans, amp in the trunk), then the output wires from the head unit share a common ground. This common ground is terminated on those 2 brown wires that get screwed on to the back of the radio heatsink.

You have probably seen pics with early model E30s showing an external fader knob. That fader was how a 2 channel radio drove 4 sets of speakers in the early model cars.

In common ground 4 channel cars, the headhunt wiring included a 2 to 4 channel adapter harness that replaced the fader. One end of this adapter plugs into the fader socket in the wiring harness. The other end is a rectangular connector with 4 blades labeled LH (links hinted = left rear) and RH (rechts hinten = right rear). Those are the rear head unit output connections that get sent to the amp in the trunk.

Here is a standalone picture of the 2 to 4 channel adapter, part number 61101388934


Note that there are no ground wires in that harness - on either end. You can tell what the head unit output wires do from the color coding:
blue head unit wires are for the right channels
yellow head unit wires are for the left channels
blue or yellow red striped wires are for the front channels
blue or yellow black striped wires are for the right channels

Now regarding the BMW Sound System wiring, those head unit outputs get routed to your blaupunkt trunk amp harness - NOT TO THE SPEAKERS. It's about 90% certain that a 30 year old unserviced power amp is fried. You can either (1) rebuild it, (2) bypass it and run headunit only or (3) bypass it and replace with an aftermarket 4 or 5 channel amp. @Rontgen's post on Luke's amp bypass thread beautifully captures the bypass you need to do for case 2.


For case 3 you route the yellow and blue wire pairs to the aftermarket amp's speaker level inputs, and the aftermarket amp's outputs get wired to the black and grey striped wires that go to the four speaker sets.

Here are the power amp output wiring colors (probably posted for the 135th time lol)
grey amp wires are for the front speakers
black amp wires are for the rear speakers
grey or black wires with red stripes are left channel
grey or black wires with violet / purple stripes are left channel ground
grey or black wires with white stripes are right channel
grey or black wires with brown stripes are right channel ground


the three remaining power amp wires are self explanatory, red for battery, white for amp on/off and brown for ground.

FYI I'm working on a couple of plug and play adapter harnesses for all this so no wire cutting is needed, but will be a while. First install will be Cosmo, my 86 Cosmoblau 325. It will be running an Infinity REF 4555A 5 channel amp and a JBL 1224SS trunk sub.

for completeness, here's a 1986 BMW Sound System schematic for TWO CHANNEL RADIOS showing the wiring for the radio, amp, speakers and power antenna. Note the radio output wiring is common ground.


Here's the same set of schematics for a 1989 late production BMW sound system car with FOUR CHANNEL RADIO wiring. Again the radio output wiring to the power amp is a common ground setup.

Finally, here's an 1989 4 CHANNEL RADIO ONLY late production schematic. Note each speaker has it's own ground wire. Early production is electrically the same with some harness connector differences


NOTE The 1989 325i / 325is electrical troubleshooting manual has 4 different radio + amp schematics based on early vs late production, radio only vs BMW Sound system. Make sure you're looking at the right version for your car!
-- 2 channel (up to early 88 or so) or 4 channel radio
-- radio only, or BMW Sound System with amp
-- coupe/sedan or convertible. Convertibles with BMW Sound System do not have rear tweeters, or crossovers on the rear speakers.
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reelizmpro: I will always be an e30 guy.. I still do all of my own labor
TrentW: There's just something so right about a well-built M20 in an E30
e30m3s54turbo: I save my money for tuner parts.

Last edited by bradnic; 06-30-2019 at 11:32 AM.
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