Radio Wiring and Amp Bypass

[StereoInstaller1]

My car is a 9/87 build date, with 8 wires coming from the fader (premium sound), so for my case, running new wires to the front and repurposing wires for the rear speakers was suggested.

88 and 89 were likely equipped with the dash mount fader, that means front and rear speakers are wired to share a ground (its "negtive" BTW, not "ground", just so you know) on each side, and that isnt acceptable for an aftermarket deck.

The trick is this: you have to have 8 speaker wires behind the deck. If you don't have 4 pairs of wire, its not going to work right. Read your install guide, this applies to all modern decks.

So, what to do?

On the super early cars (84/85) the ground junction is under the front seats, on somewhat later cars that junction is inside the dash, on much later cars (like yours) that ground junction is in the harness about a foot down the harness.

So, 88-90, pull the harness out of the dash about 18", (meaning you may have to untangle it from the rest of the dash harness to get enough out) and unwrap it.

Once you get enough unwrapped, you will see the solid yellow (gelb) and solid blue (blau) only go from the deck to the fader, so remove those.

Once those are out, keep unwrapping, you will find a point just past the "branch" where the grounds junction. The two left grounds are connected to a brown/black that goes to the fader, the two right ground do the same.

So, once you unwrap the harness, you should find those two ground junctions, cut them so the wires are as long as possible.

Once you have those ground junctions you should have 8 speaker wires behind the deck, so no need to run wires at all.

Next, lets talk about the tweeters...first, are you using Premium mids with them? If not, what are you using as a passive crossover? Some form of passive crossover is a necessity, the stock Premium setup has that crossover built into the midwoofer, thats why it has 4 terminals.

HTH
Luke

[tkeenan]

Once those are out, keep unwrapping, you will find a point just past the "branch" where the grounds junction. The two left grounds are connected to a brown/black that goes to the fader, the two right ground do the same.

So, once you unwrap the harness, you should find those two ground junctions, cut them so the wires are as long as possible.

Once you have those ground junctions you should have 8 speaker wires behind the deck, so no need to run wires at all.

Next, lets talk about the tweeters...first, are you using Premium mids with them? If not, what are you using as a passive crossover? Some form of passive crossover is a necessity, the stock Premium setup has that crossover built into the midwoofer, thats why it has 4 terminals.

HTH
Luke

I think I'll just run new wire to the front speakers. I don't really understand your explanation. I'm I understanding that I can have 8 speaker wires behind the dash. Whereas, I thought I only had 4, which are repurposed ones anyway - the ones from the fader to the amp.
My original question was whether or not I could pull the soon to be useless old front speaker wires and re-route them. Just being cheap as I don't want to have to go buy new speaker wire if I can get some good ones for free. I already messed with that a little and realized it's not worth my time.

I've the tweeters in the door. I think I'll reuse them. Actually, I hope I can reuse it, and all my other speakers minus 1, as since I bought the thing in 2010 I've only been listening to talk radio out of one speaker. The election talk pushed me over the edge though.

[tkeenan]

On my car, 9/87 build with premium stereo and fader, I've got a gray/red wire that is constant 12 Volts out of the dash, instead of the red/green as spec'd in the wiring diagram. I do have a red/green wire, I just have no idea where it goes to - it does not go to any of the speakers, and doesn't come out where the amplifier was in the trunk.
My constant dash wire, gray/red, does not kick out 12 volts in the trunk, and the same color is used on the left front speaker, as spec'd in the wiring diagram.
Maybe someone could clarify this for me.

Edit: so I found out that the red/green works for illumination. Strange though. You think it came like that from the factory? The former install looked like a disaster...

[Kershaw]

I was given a Continental TR7412UB for my birthday recently and I am trying to install it. I have premium sound, 6 wires, with the fader. The back uses a standard ISO radio adapter, 16 pin.

So my issue is, 1. When I connected my new stereo the same way as my old stereo, it didn't work. My old stereo uses a common ground and 2 leads, L and R. The TR7 uses a ground for the stereo, and then each side/speaker needs a + and -. I've been trying to get any music to play, but I've been having no luck. 2. I misread another thread (that says the same thing about this one, with 8 wires, cut the fader off) and I cut the fader wiring. That's not the biggest deal, I left enough to wire back on if need be, but that's where it is.

So how do I get +/- for each corner and retain the stock amp? Options?

Edit: I removed the amp and ran new speaker cable to each corner. Sounds great.

[Grackle]

First, let me say this is NOT applicable to all E30s. Generally, Late Model (88+) will have this wiring on premium sound cars. IF you have a fader in the dash, this MAY work: you need to unwrap about 8" of fader harness to see if you have 4 pairs of speaker wires, as some cars have only 6 wires, not 4 pairs (8 total) so if this chart does not apply PERFECTLY to your car, don't use it.

Quick disclaimer: this is not idiot proof. You mess it up, don't whine at me, I do not care.

If this saves you countless hours of hassle or you are just feeling generous, feel free to paypal me a tip. Add "@gmail.com" to Stereoinstaller1 and I promise to only use the money for projects on my car.


OK, here is the info.

Obviously, what you do here is simple: connect the "deck" wire to the "dash" wire, then back at the trunk, connect that "dash" wire to the "speaker" wire.

This is not rocket surgery, boys. Get it done.



Aftermarket-----------Dash Wires-----------Speaker Wires

RF+ Grey--------------Blue/Red-------------Grey/White
RF- Grey/Black--------Brown/Orange--------Grey/Brown

LF+ White------------Yellow/Red------------Grey/Red
LF- White/Black-------Brown/Orange--------Grey/Violet

RR+ Violet------------Blue/Black------------Black/White
RR- Violet/Black-------Brown/Orange--------Black/Brown

LR+ Green------------Yellow/Black----------Black/Red
LR- Green/Black-------Brown/Orange--------Black/Violet


(+12V Unswitched) Yellow----Red/Green (Changes to Yellow at C302)

(+12V ACC) Red-------------Violet/White (Changes to Voilet/Grey at C302)

(Ground) Black---------------Brown (may also be Brown/Black)

(ILL) Orange-----------------Grey/Red (Changes to White at C302)

(P ANT) Blue-----------------White (this is one of 2 white wires)

(AMP REM) Blue/White--------White (this is the one in the same harness as the speakers)

Luke

This is driving me crazy. I have my car all apart and I still can't sort this. I don't have any twisted pairs, or the brown/orange wires, nor do I have the blue/brown wires that should be ground. No twisted pairs. I have chased the factory wiring all the way to behind the gauge cluster with no luck. Car has an aftermarket Pioneer deck that was installed at a shop according to the previous owner. Whoever did it capped off all the - outputs from the stereo.

The stereo worked when I bought the car and then quit a couple months ago. If I run a jumper wire from the negative terminal on one of the front kick panel speakers to a negative output from the head unit, all the speakers start to work, though the head unit and the jumper wire gets hot. What in the world is going on here? Car is an 1986es.

ETA: The car has a 6 wire fader in the it.

[Grackle]

Throw up a picture...Im gonna have to write a better tutorial for early cars

I gave up. I have a six wire fader and no grounds. I just finished up pulling all the speakers and running new OFC wire. I have a NIB pair of Pioneer 160W 6x9's that are going into the rear deck once I get the riser rings I ordered. I tested them out yesterday and it sounds 100X better then it did when it was working with the factory stuff. To be fair, since someone was in there messing around to install the Pioneer head unit that is in the car, who knows what they did to it.

[VWguyBruce]

Another successful amp/fader bypass on my late model coupe. Many thanks to the OP and everyone else that assisted in making this thread what it is.

Now to hunt down the bad driver in the rear....

[Rontgen]

I want to do a factory amp bypass on a late ‘89 with premium sound with no fader. Is thing a good diagram to use?

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

Thanks!

[bpiersma]

Forgot to add:

There is no in-dash fader.

[Flexx]

I used this and it worked out well.

I own a 89 325is with premium sounds, amp and no external fader and was wondering if that was all you did?

I have the same set up but my sounds good at start up but 2
Mins in the sounds starts to fade.

I have 4 sets of speaker wires, no orange/brown wires but the positive and negative wires wrapped both for front and back speaker wires to
Make it easy.

Did you follow the write up?

[george graves]

Stock amp is on the driver's side of the trunk, on the back side of the wheel wel, under a carpeted panel. Did your car had a "fader" in the dash?

[HEIS83]

Stock amp is on the driver's side of the trunk, on the back side of the wheel wel, under a carpeted panel. Did your car had a "fader" in the dash?

Yes there is a fader in the dash, but PO had an aftermarket stereo and the fader wires had been cut. What is strange is that the new speakers/head unit worked great for a few months and then crapped out randomly one day. ill double check the trunk again tonight and see if I can track the amp down.

In researching I didn't find any fuses that would be related to it and if one was and it went, then the whole stereo would go.

[george graves]

So, this might help a bit. But some amps don't play nicely with shared grounds - or different ground on the speakers vs the amp/deck. And the "factory fader" can be a know problem. But as you said, it was cut out, but perhaps the wiring was the issue? It's too early in the AM for me to think ;) Hope that bit of trivia helps!

[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!

[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.