Understanding E30 speaker and amp wiring

[jhaurimn]

2) if you have the trunk amp, the speaker grounds are connected to the amp outputs, not the amp chassis. the amp chassis is grounded separately. the radio chassis is also grounded separately, and only the positive radio outputs are used.

This ended up being the issue, they werent kept separate. Apologies I didnt/couldnt clarify this sooner. The car had a bad battery which I attributed the radio issues with. Turns out it was a different issue all together. Glad it wasn't worse because the heatsink on the radio got insanely hot.

[bradnic]

Hi, coming out from retirement to post a correction on the original post. For the picture of my car for the older 2 channel amp bypass, make sure you only connect the speaker negatives together. (the right most bundle in the picture) In my example, I had the radio ground paired up with this, which was causing my headunit to overheat and volume would eventually go down and silent after a few minutes as it heated. Youll want to remove the ground from that bundle and either cap it, or attach it to a nearby ground location.

updated the original post. need to be clear on which grounds you're talking about though - it's easy to get confused. The speaker ground connections on the actual speakers vs the radio and amp grounds. with a no-amp system the speaker grounds are the same as the output ground connections on the radio. that's not the case on a BMW SOUND SYSTEM setup with trunk amp. you can see all of this in the schematics:

1) in a no amp system, the speaker grounds are connected to the radio outputs, not to the radio chassis. the radio chassis itself is grounded separately.

2) if you have the trunk amp, the speaker grounds are connected to the amp outputs, not the amp chassis. the amp chassis is grounded separately. the radio chassis is also grounded separately, and only the positive radio outputs are used.

If you read the above carefully, you'll notice the speaker grounds are never grounded to the chassis directly in either setup.

so yes, on a BMW Sound System setup with trunk amp, keep the output ground wires from the radio separate from the amp output ground wires (which are also the speaker grounds).

[jhaurimn]

Hi, coming out from retirement to post a correction on the original post. For the picture of my car for the older 2 channel amp bypass, make sure you only connect the speaker negatives together. (the right most bundle in the picture) In my example, I had the radio ground paired up with this, which was causing my headunit to overheat and volume would eventually go down and silent after a few minutes as it heated. Youll want to remove the ground from that bundle and either cap it, or attach it to a nearby ground location.

[zaq123]

Maybe someone can help me to figure this part. I'm trying to connect stock CM5908 stereo to aftermarket amp. My late e30 had no stock amp. I'm connecting CM5908 speaker outputs to hi-level inputs on the amp and for some reason amp doesn't like it (it shuts off after a few secs). I discovered that even though CM5908 has 4 chan. 8 wire speaker outputs, all 4 speaker "-" are actually connected to the chassis ground internally in the stereo and as a result to the car ground. Could it be that the amp doesn't want to see hi-level input signal with"-" leads on every channel being grounded?

figured it out. My Kicker KEY amp didn't like to be turned on by only hi-level speaker input signal from the CM5908 (one of the Amp's options where remote turn-on wire can be left taped off and dip switch set on DC). Connected amp's remote turn-on blue wire to 12V, switched the dip switch to +12V and all is good. Actually sweet little amp, fits into the Airbag ECU bracket perfectly and even mounting holes on the bracket work with a little modification). Just had to extend LF blue wires from the middle of the dash to the amp (mounted in the airbag module location, LH side of the dash), the rest of OEM wiring worked perfectly as they all go through the left side of the dash. Basically , CM5908 speaker outputs to the AMP hi-level in, AMP speaker outputs to stock wiring. AMP is only 200 W so fits perfectly for premium sound speakers without straining the amp (45W/ea.)

https://www.kicker.com/app/manuals/47KEY2004.pdf

[zaq123]

Maybe someone can help me to figure this part. I'm trying to connect stock CM5908 stereo to aftermarket amp. My late e30 had no stock amp. I'm connecting CM5908 speaker outputs to hi-level inputs on the amp and for some reason amp doesn't like it (it shuts off after a few secs). I discovered that even though CM5908 has 4 chan. 8 wire speaker outputs, all 4 speaker "-" are actually connected to the chassis ground internally in the stereo and as a result to the car ground. Could it be that the amp doesn't want to see hi-level input signal with"-" leads on every channel being grounded?

[PNWE30M50]

I wanted to try and help others in return and thought maybe a video could do that.

Luke's massive original amp bypass thread helped me out a lot. So much reading! I posted over there as well in case others are looking.

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.

Hope this helps someone

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

[nando]

is it in the trunk next to the antenna just like a sedan? you have to pull the carpeting off the driver's side.

also, is your KE83ZBM for sale? Does it work?

[Scottie409]

Hello, am replacing the head unit on my 91 318i Converible with a Pioneer CD bluetooth unit and removed the KE83ZBM and didn't realize there was an auxiliary amp on this vehicle.
Where is the amp located on a convertible?
thanks in advance
Scottie409

[nando]

yeah, I wondered. I think I left it attached to the radio that I ended up selling for probably $5. Doh! I see it's still available new, I should order one before it goes NLA.

I'd pat myself on the back, but I feel like I dodged a bullet. When I first looked at it again, I had no recollection of how I'd wired it originally and feared the worst (it was almost 20 years ago, lol). But earlier when I was even younger and especially dumber, I cut a huge hole in the hood of my '67 Dodge Dart to put in an ugly hood scoop. Ugh. I regretted it instantly, and ever since then I've had an aversion for permanent, irreversible mods.

It's funny because of course when I originally did this, I didn't listen to tapes - I wanted a CD player, and later MP3s were the thing. The stock stereo I didn't assign any value to. Now I mostly listen to the radio, and I don't exactly blast the tunes. I've had the blank plate for nearly 10 years now, and honestly I'd be pretty happy with a stock, unmolested sound system vs nothing at all. Now I kind of want to make a mix tape of some 1990's music, lol.

[bradnic]

BTW you’re missing the 2 to 4 channel adapter harness. Pic and part number earlier in the thread.

nice job keeping the original connectors and just splicing in the ISO bits for your aftermarket. I did the same thing on my vert years ago so it was super simple to restore it back

[bradnic]

That’s a KE83ZBM 4 channel pioneer. Switch to a 5908 slider and you can rock the Cantaloupe BT board. Jay’s not doing them anymore but I am doing another production run later this summer.

[nando]

yeah, it's my ix, it had premium sound - but I have no recollection of what the original stereo was (might be able to find it in old pics). I think I can just repair the wiring, but I might be missing a pigtail/adapter or whatever was plugged directly into the stereo.

actually, I have *one* pic of the stereo (sorta) - from the day I got the car in 2002, lol:

http://www.325ix.com/pics/2002/05-31-02/MVC-272F.JPG

[bradnic]

nando !!!!! damn son. Happy to help get your setup back. this is your IX right? you've got premium sound I think.
if you want the wiring back 100% stock just hunt on ebay. Otherwise I have some of jay's repair connector kits.

[nando]

Man, I fee so stupid for hacking up my original wiring and putting in a shitty aftermarket head unit (long since gone - I've had a blank plug in that spot for years now).

Thinking it might be time to go back to all OE. All of the wiring is still there I think, but I don't remember exactly what I cut and removed. I gave away the stock premium radio for a song too! But it looks like I still have options. I'm pretty sure I left the amp inside the car (I hope!). I actually have a full harness from my '88 ix parts car, but that had been cut a bit as well.

edit: well, apparently 21 year old me wasn't as dumb as I thought. I did cut a couple wires - but I actually left all of the original harness and plugs there. I remember now - ran separate wires from the stereo to the connector in the trunk, so all of the wires to the speakers, head unit, etc are original and untouched.

http://www.325ix.com/photos/cache_big/2021/OE%20Stereo/IMG_2133.jpg
http://www.325ix.com/photos/cache_big/2021/OE%20Stereo/IMG_2134.jpg
(looks like image linking is broken on this forum now, ugh)

The bad part is I can't find the amp (it's not in the trunk). I thought I had it somewhere, but I dug through my giant pile of parts and didn't see it. There's a spider infested box I haven't looked at in years, it might be in there, but it's probably water damaged by now anyway.

At least repairing the original harness should be dead simple! All I have to do is remove the butt connectors and splice the stock wires back together. I'll probably want to pull out those speaker wires I put in, but they aren't hurting anything if I just leave them either.

[bradnic]

just received my power amp connector from RyanBelton . It is very well made and documented. Highly recommended.