Late factory head unit details

[Tremelune]

I've decided to put an aftermarket stereo in my '90 M3 (in the glovebox) with premium sound, and in the process pulled the factory unit out. The late-model E30 had the "Pyramid" stereo (Alpine CM5908). The audio outputs are routed through the big black connector such that I don't think I'll have to cut any wires in the harness. I found some wiring info here. I think it will be slightly different for each model depending on vintage and the existence of a factory amp.

Speakers - Early
Front
LF - Yellow/Yellow & Brown - +/- [The yellow twisted pair at connector C212]
RF - Blue/Blue & Brown - +/- [The blue twisted pair at connector C218]

Rear
LR & RR - Yellow & Black/Blue & Black - +/+ [The blue and yellow pair at connector C244. The minus connection for these speakers is in a splice to the LF and RF minus wires.]

Speakers - Late
Front
LF - Yellow & Red/Yellow & Gray - +/- [The yellow twisted pair at connector C212]
RF - Blue & Red/Blue & Gray - +/- [The blue twisted pair at connector C218]

Rear
LF - Yellow & Black/Yellow & Brown- +/- [The yellow twisted pair at connector C245]
RF - Blue & Black/Blue & Brown- +/- [The blue twisted pair at connector C244]

Others
The White and Yellow pair ending at C215
White is the lights on input and connects to a Gray & Red wire at the connector.
Yellow is constant power and connects to a Red & Green wire at the connector.

The single White wire is the antenna up [and amp on if yours had one] output.

I'm having a hard time seeing the exact color of the remaining unconnected bundle but I think it's the switched power and ground connection. See if these colors match up.
Violet & Gray - switched power
Brown - Chassis ground


One final thing to remember. If the radio has lost power, you'll need the radio code to input.

Here are some photos I took along the way:





















Here are some shots of the screw mechanism that holds the head unit in. I used a pointy knife to open the plastic tab, then a 5/64 allen key to unscrew the mechanism. It doesn't fit perfectly; you may need to insert it at a bit of an angle to get a better purchase inside the screw.





Here's a shot of the back of the big black connector...The interesting bit is the re-routing of some of the audio audio outs.


Another shot of the black connector, this time the side that's in the car. You'll notice that some wires simply aren't attached to anything on the other side of the connector.

[Tremelune]

A nice related thread:

http://www.r3vlimited.com/board/showthread.php?t=138412

[Tremelune]

I've learned things about my particular setup ('90 M3)...Due to the way the speaker negatives are combined at the back of the head unit, I could not see a way to install an aftermarket head unit without cutting the factory speaker wires or running my own. If you install an aftermarket head unit, you need to cut the factory wires at the amp, too (or run your own), which means you might as well bypass it entirely--The average modern head unit will be louder and cleaner. I read about it a dozen times, but it wasn't clear until I saw it with my own eyes, so here are some shots of the factory wiring.

Here you can see how the speaker negatives are joined at the head unit. All four speaker negatives are (eventually) connected to each other.




This is another spot where the other speaker negatives come together. This is screwed into the back of the factory head unit chassis.




All the speaker negatives need to be cut and isolated from one another. When you trace back the speaker wires into the dash far enough, they form four distinct twisted pairs that go all the way to the factory amp in the trunk.




Here's a shot of the factory amp in it's home above the left rear wheel well. You'll need to pull out most of the carpeting to expose it. You'll need to remove it to do pretty much anything. Two of the three screws required to remove it are visible on the red paint.




Here's the third screw (top right, visible against the red paint).




Here's the amp out in the open, on the right. Note: The small box (on the left) attached to the same bracket is not related to the audio system--Don't fuck with it.




Here is the wiring to the amp harness after pulling back a few inches of tape. You can see the manner in which the four speaker negatives are joined at the amp as well.




Once again, if you peel back the tape far enough, you will see the four distinct twisted pairs of speaker wires coming from the head unit (the colors will match). There are four additional twisted pairs that go to the speakers (of different colors than the head unit wires).




This is a shot of the patched/byassed wiring. I used a connector to facilitate future changes, but it's not necessary. All you need to do is cut out that common ground point, and join the speaker pairs from the head unit to the speaker pairs coming out of the amp (as described in the thread linked earlier), and you should wind up with a standard four-channel setup. Leave the factory amp unplugged.

[Tremelune]

Next step will be to run low level (RCA) signals over the wires to the trunk into an aftermarket amp, which will then feed the "real" speaker wires.

[Tremelune]

Oops, the handy threads I had alluded to earlier are these (they're stickied):

Radio Wiring and Amp Bypass

How to install a killer stereo

[StereoInstaller1]

Great pics, great wording..good job!

Oh yeah, nice work too. I have a ton of stuff to add to the tutorials at some point, when I add them to our site and here on R3V. May I have permission to use your pictures?

Luke

[Tremelune]

Of course, be my guest.

[Staszek]

I wanted to bump this thread because I went through this install last weekend and I wish I had this. Really nice and really clear!