This is for those without a lot of car electronics experience, and they want to take out the stock BMW tape deck headunit out and put in an aftermarket stereo. when came time for me to do it, i could only find tidbits, and procedures from going from one aftermarket thing to another. hopefully, this will help those out there like me. Many thanks to Dudesky too, without his help, I would have never got that damn thing working.
Two things make this difficult for the novice, central grounding of the speakers, and the stock amp. the stock amp is located in the trunk, on the left wall right in front of the power antenna. pull down the trunk side and you will see it, but luckily, we wont need to remove it or the antenna, we just need to take it out of the speakers circuit. In my first E30 the amp was garbage, and everytime it hit a bump, the sound crackled. Yup, it was the amp, because the headunit worked fine in my grandmother-in-laws Mercedes, and when the amp was taken outta circuit it sounded fine.
I tried to use the amp with the new headunit in my second E30, but it sounded like shit. so forget about it. also, this is how it was for my E30 (and my last one as well), but of course I have to say that your wiring may vary!
Also, be sure to disconnect the negative terminal of your battery prior to any electrical work.
First we need to figure out what we need and have in the dash. For most aftermarket headunits (mine was an Aiwa, now I have an Alpine
) the color code is:
Black - Ground
Blue - Auto Antenna
Blue/White - Amp Remote on (wont mention this again, if you need this then you shouldnt be reading this! Tape this off and forget about it)
Yellow - Constant Power
Red - Switched/Ignition Power
Grey - Positive Front Right
Grey/black - Negative Front Right
White - Positive Front Left
White/black - Negative Front Left
Purple - Positive Rear Right
Purple/black - Negative Rear Right
Green - Positive Rear Left
Green/Black - Negative Rear Left
Your aftermarket wiring harness may vary
so we need to take those and connect them to the wires that are coming from in the dash. In there it is a mess of wires that seem to loop retardedly. dont worry about how they are wired, we are going to undo all that anyway. There are some extra wires that come out of the headunit, 1 pair is not used, the other i dont know what its for (perhaps amp remote on, didnt need it). you basically need only the wires that are used in your new harness. Before you connect them though, follow the procedure below for finding the correct negative wire.
Purple/White - Switched/Ignition power - connect to Red on aftermarket harness
Brown/Black - Ground - connect to Black
Red/Green - Constant Power - Connect to Yellow
White - Power Antenna - Connect to Blue
Grey/Red - Dont know, tape it off and forget about it.
This is where it can be a little tricky. The right side speakers (front and back) have the same wire color for negative, Blue/Brown. The left is the same way, Yellow/Brown. Ill tell ya how i figured it out in a minute.
Yellow/Red - Positive Left Front
Yellow/Brown - Negative Left Front
Blue/red - Positive Right Front
Blue/Brown - Negative Right Front
Yellow/Black - Positive Left Rear
Yellow/Brown - Negative Left Rear
Blue/Black - Positive Right Rear
Blue/Brown - Negative Right Rear
As you will notice, Red is the front speakers, black is the rear speakers (speaking about the secondary wire colors), and brown is negative, while Yellow/Brown is the left, and Blue/Brown is the right. So it makes a bit of sense there.
Picture of the stock headunit wiring:
Sorry, forgot to take pics of the wiring I did in the dash.
- To find the proper negative lines for each of the respective speakers I used a 9V battery and a 12V light bulb, like the ones used in your tail lights. Go to the trunk where the amp is and find the wire bundle that has twisted wire pairs that match the wires from the dash. You will also see other wire pairs there; we will discuss those in a second. Those are the wires going from the speakers to the amp.
Cut into one of the twisted wire pairs that match one of the pairs of wires from the dash. Attach the 9V battery here (and make sure nothing is attached at the other end, and the bare wires are exposed, but not touching anything). Then go to the dash, attach the positive wire to the light and then try the negative wires. Once you find the correct one, you can instantly assume that the other wire that is the same color is the opposite speaker, in this case, the opposites are front and rear. Do the same for the other side of the car (if you did the left, then do the right, or vice versa). When you find what the correct wires are, twist those bad boys together, then connect everything to your new aftermarket wiring harness.
The next thing to do is to cut into the lines that go from the amp to the speakers and match them up to the lines that come from the dash to the amp, the lines you just cut into. also be sure to properly tape off all the wires that come from the amp. There will also be other single wires there, dont touch em. The speaker wired pair colors are below. These pairs should be twisted together.
Grey/Red - Positive Left Front
Grey/Purple - Negative Left Front
Grey/White - Positive Right Front
Grey/Brown - Negative Right Front
Black/Red - Positive Left Rear
Black/Purple - Negative Left Rear
Black/White - Positive Right Rear
Black/Brown - Negative Right Rear
Again, these wires follow a general code for left vs right, and front vs rear. But who cares anyway?
Thus, connect the following wires in the trunk:
Grey/red and yellow/red
Grey/Purple and Yellow/Brown
Grey/White and Blue/red
Grey/Brown and Blue/Brown
Black/Red and Yellow/Black
Black/Purple and Yellow/Brown
Black/White and Blue/Black
Black/Brown and Blue Brown
After I finished in the trunk:
And thats it. After making everything nice and neat, crank that new Headunit. I used 3M Splice connectors for all wire splicing, then wrapped wire bundles with electrical tape. what you use is up to you. In all actuality the color of the wires does not matter, just as long as you get the correct current going to the right speaker, but i kept all color codes as I *believe* they were supposed to be for simplicity sake.
Also some helpful tips that helped me, courtesy of Dudesky:
Originally Posted by Dudesky
First of all, it doesn't matter if the wires are on the wrong terminals as long as you maintain that scheme on all the speakers. For instance, if front left is wired correctly and front right isn't, the sound will be out of phase. In this case, what is happening is that one side is pushing the cone out at the same time the other side is pulling the cone in; the opposing actions cancel each other out, resulting in loss of sound output, mostly apparent in bass notes. However, if they're both wired incorrectly in the same fashion, then it is the same as having them wired correctly.
Having said this, here's a few things you can do:
1) Look for a red mark near one of the terminals on the speaker itself; this usually indicates the positive leg. Or in many cases, the terminal bracket has (+) and (-) stamped on it.
2) If the speaker terminals differ in size, the larger is almost always the positive leg.
3) If neither condition is present, then observe the stock harness plug's orientation, and use that to maintain consistency through out the system.
4) If you don't have the speakers exposed, hopefully you can see through the speaker grille and see the cone itself. Connect a battery to the wires corrsponding to each speaker, at the dashboard. Observe the cone motion. If the cone moves forward, then you have the battery's (+) on the (+) wire. If it moves backward, then you have the battery's (+) on the (-) wire.
Good Luck with your install, and if you have any questions, you can PM me, but honestly, you could probably get a lot more help by asking everyone here at UB.C!
PS - I have a stock BMW Headunit for sale, wiring harnesses included
The finished product: