San Diego Qualcomm Autox had some requests on stereo install so I am reposting my DIY

2003 M3 Coupe no HK, no CD changer, March 2003 build
800 watt stereo install with front imaging and subwoofer.
150 watts each to the front MBQuart QSD 216 speakers and 500 watts to the rear sub. Fader controls front speakers and rear sub. Also added 500/1 boost potentiometer. Sirius radio is absolutely great, nice fidelity, sounds like a CD. Imaging is good with a nice front stage. For those of you that have had many stereos, you need the watts. You need the watts for the QSDs to come alive. You need the watts for the sub, because that trunk seals so tightly. Front speakers at high pass around 85 hz and sub low pass 85 hz. I have tried 12db crossover slope and 24 db. I am currently at 12 db for the sub. Did I mention that you need the watts? Don’t skimp here you will regret it, especially with these components, they really come alive with the proper amplification. BTW I spent about 40 hours on this install. A lot of that time deciding on wire and amp locations. With this DIY, I should think you can cut down your install time considerably.

Equipment list
JLAudio 300/2 amplifier
JLAudio 500/1 amplifier with boost potentiometer
JL Audio 2 gauge power cable to a 4 gauge split for two amps, JLAudio miscellaneous, like ring gold plated ring grommets
(2) JL Audio spliters 2 to 4 gauge
JL Audio 2 gauge 100 amp fuse holder
(2) JL Audio line level inputs to RCA cables for front (speakers) and rear (sub) preamp in.
(2) 9 foot (more than enough) RCA cables for speaker inputs and sub. Also male to male connectors for RCA cables
MBQuart QSD 216 speakers, includes 2 way speakers with crossovers.
Diamond Audio 12 inch M6 subwoofer, M6 12D2 wired in series for 4 ohms impedance
Corey’s 3 series enclosure
3 Series (E46) Sedan & Coupe w/o Nav with CD radio (2003-On)
Sirius Receiver 84 11 0 141 981
Roof Antenna Kit 84 11 0 141 979
Installation Kit 84 11 0 141 976

Honorable mention to William for his original DIY. His wiring diagram for the harness was 100% correct.

For those of you that can’t wait until the bottom to see the finished product. Her is a pick of the finished product. The rest of the pics are step by step on the install.

2003 M3 March build Sirius ready Head Unit. No stock upgrade to the Stereo. No HK, no changer. In the pics below you can see the stock setup. Empty plastic shelving

Now with the fiberglass trunk panel removed. The plugs that hold the fiberglass to the car remove by removing the center piece first. Then remove the plug. The plugs are actually two pieces. Just grab on to the center piece and remove. The rest of the plug loosens and removes easily. I destroyed one plug before I figured that out.

Stock AMP location

Amp unscrewed hooked to the wiring harness

Wiring harness for preamp output, speaker input, and +12V for amp turn on. See Williams post for detailed wiring. All wiring listed on Williams DIY are correct.

Antenna wire for the Sirius satellite radio. I mounted the hockey puck type antenna where the center hook is in the rear back deck. Just remove the hook and thread the wire through the hole. Mound the antenna facing backwards with the stickum holding to the plastic part of the rear deck hook.

Stock power wire

New 2 gauge red power wire for amps. Notice I piggy back on the stock wire. Cut the red cap on the positive cable and it will fit with the new 2 gauge wire.

100 amp JL Audio fuse assembly in corner. Modified to make a left hand turn.

Above the red wire you will see a 2 gauge negative ground cable for the amps. Perfect location with a short distance from the amps. Notice the drill where the hold needs to go

IMPERITIVE that you spend time scrapping away the coating on the metal. The coating is non-conductive and is there to prevent rust, etc. Get a good file and scrap it away around the hole you drilled. I used an ohm meter to check and make sure I had a good connection. You can see the shiny portion around the hole indicating the scraping.

Torque it down nice and secure with a screw and nut

Remove carpet (the one with the rubber backing) and place amps in front of trap door for the mobile utility unit. Sub amp on the passenger side and speaker amp on the drivers side. Place there for now to, but do not drill yet. You are placing there in order to size and cut the power wires.

T20 torx required to remove screws from the door handle, behind the airbag sign and behind the open door latch.

Remove door panel by using a door panel removal tool with a towel wrapped around it

Door panel removed

Stock speaker location

Speaker with flange. KEEP flange, you are going to use the flange with the MBQuart QSD 216 speakers. I tried it with and without the flange. Much better with the flange because without the flange the back portion of the grill will interfere with the rubber surround of the speaker. The flange creates a wider area for the speaker and allows the clearance. Also no cutting will be required with the flange, it is a dropin. Without the flange a little bit of plastic cutting will be required.

Comparison of stock versus Mbquart QSD 216

Tweeter, I used the angled assembly that came with the QSD 216 tweeters. I angled the tweeter back and up towards the center of the car. Better imaging.

Flange in

Woofer in. Notice the clips I used to secure the speaker. They actually come with the MBQuarts. I just modified them on the vice to fit. Vice and hammer is all you need.

Diamond audio M6 12” woofer. Very heavy woofer using Corey’s enclosure. Make sure you use T type nuts to secure the woofer. DO NOT USE WOOD SCREWS. At home depot you can get a nut which has spikes point back toward your screw. You drill 8 holes for the subwoofer and then secure the nuts with the spikes in place on the inside of the enclosure. Wire your sub for 4 ohm and place in the enclosure. Now you torque down your screw in a figure 8 pattern to secure the woofer and (this is very important) create and air tight enclosure. With the spiked nuts you can tighten them extremely tight and create and nice sandwich seal for the subwoofer. After tightening push the subwoofer in, you should be able to feel it air tight. It should feel like you are pushing against a balloon. If it goes in to easy, then you do not have an airtight seal. You absolutely need this for good tight base. You will know when you have a good seal, when you push in that sub.

Creating shelves for the crossovers using ¾ inch plywood and painting black.

First shelve and crossover in place. Underneath the shelve is the Sirius radio tuner which I also added. The place where I put it is in the recommended place with the install kit.

For securing the wiring I used the electricians spring loaded twist caps. Easy to use. I also tagged and cut all the wires I needed. I used the midrange wiring for the tweeters, since the stock wiring looked thicker. See Williams post for details on determining the wiring layout. For the preamp out I used line level to RCA cable jack that JL audio sells. Very convenient with the spring loaded twist caps. I followed the stock wiring with twist ties up towards the amps.

Other side of vehicle now showing the blue speaker wire for the sub

Now it is starting to look like an install, I can see the light at the end of the tunnel.

For you autox guys, I added a rubber bungy strap, just incase.

Cut the carpet (the one with the rubber backing) to exact specs.

Took off road assistance sticker and added MBQuart plastic logo.

Removed back seat and added the Bass Boost potentiometer from JLAudio for bass adjustment. For now I have it coming up under the rear armrest on the drivers side.