Radio Wiring and Amp Bypass

[quasi mofo]

Added some sound damping to my car and realized that I have no sound coming from my right side speakers.
I have a 1989 325is. The stock speakers and wiring are in place, but the BMW amplifier has been removed. After pulling the trunk liner and the aftermarket stereo, I found 3 RCA cable pairs that run from the dash to the trunk and 3 runs of stereo wire. One of the stereo wires terminates behind the stereo and two were coiled up under the rear seat.

As a novice E30 archeologist, I'm guessing that one of the PO's replaced the stock head unit, pulled the stock amp and bypassed the stock wiring with an aftermarket amp and new stereo wire. I guess they were using a 3 channel amp, maybe. But then a more recent owner pulled the aftermarket amp and reused the stock wiring. This is where I seem to be having a problem. This is the nest of wiring that is behind the stereo head unit.





So in the second image, the PO has the green/black and purple/black negative right front/rear speaker wires connected to this second harness. The positive green and purple wires aren't connected to anything.

Any advice on what I should to do restore sound to the right side speakers? Thanks in advance!

[Aleman]

I’m new to all this, but this doesn’t seem right to me, I have all the wires from my new head unit w a black strip left untouched and I have L/R blue and yellow solid wires left. I don’t know what these go to but I assume front or rear speakers?

SOLID YELLOW = LEFT FRONT speaker.
SOLID BLUE = RIGHT FRONT speaker.

[Slybeanx]

I’m new to all this, but this doesn’t seem right to me, I have all the wires from my new head unit w a black strip left untouched and I have L/R blue and yellow solid wires left. I don’t know what these go to but I assume front or rear speakers?

[bradnic]

Found out what the two mystery wires go to. Nothing in the E30.

https://www.r3vlimited.com/board/sho...69&postcount=6

yes they were for a 'dot matrix' feature. lots of speculation, but the post you linked to was probably close - just a way to display radio or cd track number info somewhere else, probably on the 5 series as mentioned. I've never seen evidence of such a feature back then, but it was certainly common in the early to mid 2000 timeframe.

[Aleman]

I posted this in another thread I made, but maybe it makes more sense to post it here.

Does anyone know the best way to do the amp bypass mod while leaving the original wiring intact? I know, needlessly complicated, but I don't want to modify the original wiring so I can revert back to stock without having to re-wire anything later.

I have an amp that isn't good I'm going to attempt to use for this. The issue I've come across are the common ground speaker wires coming from the radio (this is a 90 325is with premium sound); the 2 yellow/brown and 2 blue/brown wires that combine into the single brown/black wire just before the amp connector. I read there shouldn't be common grounds for the speakers for the aftermarket HU (should be floating ground instead). So do I just connect the positive wires together inside the amp and leave the grounds connected as they are in the amp? Does the amp need to be powered on for the grounds to do whatever they need to do or should I terminate the power and remote turn on wires?

I used my multimeter to test the grounds at the amp connector for continuity and they don't have continuity. They go through circuitry in the amp, and I don't know exactly how the circuitry is configured and what it consists of or what it does exactly.

Maybe I should just install a floating ground adapter inside the amp.

One way to do it is to use a ton of Tap Splice Connectors. You can pull the amp out, and then bridge from speaker loom to radio loom with one of these splice connectors on each wire. No cutting.

[Aleman]

Found out what the two mystery wires go to. Nothing in the E30.

https://www.r3vlimited.com/board/showpost.php?p=4763969&postcount=6

[Aleman]

I checked all the wiring diagrams and none of them covers the cm5908. Anyone know what the blue/gray and white/brown wires hardwired from the HU should connect to? Nowhere. Those don't apply to the E30. Just wrap up that cable and leave it disconnected from anything. That 2-wire connector is for the E28 installation and seems to be for an external digital display in that vehicle. Those colors aren't on the 89 wiring diagrams.

Also, does the yellow/brown HU wire connect to a solid brown wire? Yes. And the blue/brown HU wire connect to a solid brown wire? Yes. The 89 diagrams only show the yellow HU wire connecting to yellow/red amp wire and blue HU wire connecting to blue/red amp wire.

I see the yellow HU wire connects to the yellow/bk and the blue HU wire to the blue/bk. Once I get it hooked up and working I'll post a clear chart for the next guy.

Sent from my smart phone using Tapatalk

[bradnic]

@bradnic
How do you know if your amp is fried? Symptoms?

-squealing in one or more speakers
-distortion from the speakers at less than full volume
-low static noise from one of more speakers even when nothing is playing in the headunit
and of course
-no sound

Unfortunately to be 100% sure it's the amp and not the radio, you need to do the amp bypass or swap the headunit out. So it's not uncommon to fix a radio and then later find the premium amp needs service too

[Aleman]

@bradnic
THANKS! That clears up a lot of the mystery.
How do you know if your amp is fried? Symptoms?

Sent from my smart phone using Tapatalk

[bradnic]

I posted this in another thread I made, but maybe it makes more sense to post it here.

Does anyone know the best way to do the amp bypass mod while leaving the original wiring intact? I know, needlessly complicated, but I don't want to modify the original wiring so I can revert back to stock without having to re-wire anything later.

I have an amp that isn't good I'm going to attempt to use for this. The issue I've come across are the common ground speaker wires coming from the radio (this is a 90 325is with premium sound); the 2 yellow/brown and 2 blue/brown wires that combine into the single brown/black wire just before the amp connector. I read there shouldn't be common grounds for the speakers for the aftermarket HU (should be floating ground instead). So do I just connect the positive wires together inside the amp and leave the grounds connected as they are in the amp? Does the amp need to be powered on for the grounds to do whatever they need to do or should I terminate the power and remote turn on wires?

I used my multimeter to test the grounds at the amp connector for continuity and they don't have continuity. They go through circuitry in the amp, and I don't know exactly how the circuitry is configured and what it consists of or what it does exactly.

Maybe I should just install a floating ground adapter inside the amp.

You ever get an answer to this?
I did the amp bypass under the rear seat of my 90 vert. I then reversed it after refurbishing my power amp. I'm working on a harness bypass for aftermarket amps that doesn't require cutting the OEM wiring, but it will be a while.

If you're asking about getting rid of the common ground extensions at either end so you can run an aftermarket headhunt, right now you're stuck needing to mod the wiring. There actually is a 2 to 4 channel adapter from BMW that DOES preserve the individual speaker grounds. It's expensive though, and still has the German speaker connectors on it.

[bradnic]

So @Aleman you have the 4 channel common ground setup common to the later cars. basically at the head unit all the speaker grounds are terminated on those 2 brown wires that get screwed on to the back of the radio heatsink.

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.

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.

The left side of the big black connector in your wiring is what the old external fader used to plug into. In common ground 4 channel cars like yours the headhunt wiring included a 2 to 4 channel adapter harness that replaced the fader. The right side of that black connector is one end of the adapter. 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 speaker connections.

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 speaker outputs get routed to your blaupunkt trunk amp harness. It's about 90% certain the 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 pic 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 an adapter harness 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.

[Aleman]

How do I wire my CM5908 WITH the amp? On the wiring diagram for a 1989 with amp, it shows only one wire per speaker from the HU to the amp, rather than 2 (just like rontgen explains above). I think I can figure it out by trial and error as far as which of the two wires from the radio I should use per speaker. My big question is around what I see in the factory wiring. There's a harness connected to the speaker harness that looks factory given all the German language and BMW logos, but it looks like something really strange is going on there. 8 speaker wires in, 2 out. I hesitate to cut any harness, so have you guys ever seen this setup in a late model E30 with premium sound? 1990. Maybe my car had something other than a CM5908?

Thanks for any info you may share.

Sent from my smart phone using Tapatalk

[Andrew325is]

I posted this in another thread I made, but maybe it makes more sense to post it here.

Does anyone know the best way to do the amp bypass mod while leaving the original wiring intact? I know, needlessly complicated, but I don't want to modify the original wiring so I can revert back to stock without having to re-wire anything later.

I have an amp that isn't good I'm going to attempt to use for this. The issue I've come across are the common ground speaker wires coming from the radio (this is a 90 325is with premium sound); the 2 yellow/brown and 2 blue/brown wires that combine into the single brown/black wire just before the amp connector. I read there shouldn't be common grounds for the speakers for the aftermarket HU (should be floating ground instead). So do I just connect the positive wires together inside the amp and leave the grounds connected as they are in the amp? Does the amp need to be powered on for the grounds to do whatever they need to do or should I terminate the power and remote turn on wires?

I used my multimeter to test the grounds at the amp connector for continuity and they don't have continuity. They go through circuitry in the amp, and I don't know exactly how the circuitry is configured and what it consists of or what it does exactly.

Maybe I should just install a floating ground adapter inside the amp.

[Rontgen]

Did this re-wire tonight on my son’s 90 325is. The car has premium sound with no fader dial in the dash. Very bizarre wiring for what should be a very simple audio circuit.

From amp to speakers is a piece of cake and Luke’s original post is spot on. 4 speakers, 4 twisted pairs, 8 wires total. Easy.

The connection from the front of the car to the amp input is where things get confusing. Rather than sending 8 wires from the radio to the amp like any sane person would do, BMW opted to tie all the grounds together at both ends. Lucky for us, the twisted pairs still exist, you just have to untape the harness and work your way back until you find them. Keep in mind that the ground colors in the first post may not match your car. You’ll probably end up with 2 yellow/brown wires and 2 blue/brown. Just keep the twisted pairs together and connect one at a time.

Picture of our trunk wiring before we taped it all up with cloth harness tape. Hope this helps!

[HEIS83]

no amp in the trunk. right now i am waiting on the headunit to be returned so I can hook back up and troubleshoot again. I want to avoid having to re-wire the speakers but I am running out of possible solutions.