Radio Wiring and Amp Bypass

[Aleman]

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

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[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]

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.

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[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 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.

[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.

[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?

[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.

[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!

[bradnic]

I have completely updated the E30 speaker and amp wiring thread. Should help folks a lot with understanding what they need to do.

https://www.r3vlimited.com/board/forum/e30-technical-forums/car-audio-electronics/387356-understanding-e30-speaker-and-amp-wiring

[bradnic]

Did this diagram work for you? I have an early build 1990 with premium sound and no external fader.

Thanks!

There are both 2channel and 4 channel amp bypasses. The 2 channel amp bypass has fewer wires, so that table won't work for it. fully explained in the first post here https://www.r3vlimited.com/board/for...and-amp-wiring

[nando]

Finally snagged a KE83ZBM that isn't completely ragged! It probably still needs caps, a new drive belt, and to get the CODE from the dealer, but it looks to be in decent shape and the screen is good.

So now, do I really want an OE amp? It's been a long time since my stereo was stock - it wasn't that great that I remember. What's a decent drop in replacement for the 4-channel bypass? Maybe 5 channel, if I want to add a sub one day, but I'll just run stock speakers for now. I don't want to cut into the wiring more than is done already, but I could easily print my own housings/adapters..

[nando]

Finally snagged a KE83ZBM that isn't completely ragged! It probably still needs caps, a new drive belt, and to get the CODE from the dealer, but it looks to be in decent shape and the screen is good.

So now, do I really want an OE amp? It's been a long time since my stereo was stock - it wasn't that great that I remember. What's a decent drop in replacement for the 4-channel bypass? Maybe 5 channel, if I want to add a sub one day, but I'll just run stock speakers for now. I don't want to cut into the wiring more than is done already, but I could easily print my own housings/adapters..

I finally plugged it in. Needs one of the lights on the LCD replaced, but otherwise it seems like it's really clean and functional.

Once I get the CODE from the dealer, I'll get to fixing the wiring for the amp. I'm thinking I'll just skip to an aftermarket 5 channel, since I don't have a stock one anyway.

Also my original antenna mast still works! I had to clean and lube it and run it up and down a few times, but I was afraid it might be toast. I probably haven't used it in 10 years.

[PNWE30M50]

Thank you everyone! This thread really helped me. I wanted to try and help others in return and thought maybe a video could do that.

Posts #91 and #448 were my go to.

I have a 1987 325es, CM5907, premium sound, fader in dash (6 wires), and a stock amp in the trunk. Went with a Continental TR7412UB-OR, bypass stock amp/repurpose fader wires, rewire fronts/tweeters.

Please let me know if you see something I did wrong so I can fix it!!! I am also garbage at talking while filming...so sorry in advance.

https://www.youtube.com/watch?v=lXYdEnJJVnU

[e30mobber]

used this and worked absolutely perfect in my 91 325i coupe with premium sound and no fader, perfect amp delete write up and sounds fantastic > thanks guys

here’s the work> piece of cake (00=00)