Sub and Amp Installation in 1995 BMW 318ti Introduction The stock 318ti sound system lacks bass. To combat this problem, and to make myself cooler, I decided to install two subwoofers in my hatch. This is a detailed guide on everything needed to know about installing a sub setup in a 1995 318ti.
First off is the component list. To install a proper sub setup, you need the following things:
1. Amp wiring kit. This can be found for 20 dollars at the local Wal Mart, made by Schosche. This is a better deal than the 80 buck wiring kit Circuit City tried to sell me. It includes everything except the actual speaker wire.
2. Speaker wire. Make sure it is thick enough to handle all the power your amp will put out.
3. Amp. I have an MTX 311 watt amplifier.
4. Subs. You will need as many as you want. I have two.
5. Compatible head unit. You need a head unit that has an RCA output and a remote turn on wire. The remote turn on wire runs to the amp and powers the amp whenever the head unit is powered. It is the blue wire or the blue/white striped wire in the back of the head unit.
6. Box. I managed to obtain my friend’s old sub box for free. You can buy one or make one yourself.
Before you get started, check out the wiring diagram. Get familiar with that before you rip your car apart.
(Sub Diagram)
http://www.318ti.org/gallery/data/504/subdiagram.jpg Now it is my time for my personal rant. Some kids my age just don’t care about looks and don’t mind having wires lying around on their floor. I am not this way. Whenever I install subs, I make sure that every wire is completely hidden, not just under some plastic trim, but I burry it under the carpet so no trace of the wires can be found. I prefer the professional clean look myself.
Note: Before you do any fooling with electronics in your car, disconnect the negative terminal on the battery.
Note: Be gentle with interior trim. Tabs that hold pieces in place will snap very easily.
Note: I wrote this guide after I had my subs installed for nearly three years. That is why you will notice I didn’t feel like removing some trim and my wires are already in place.
Power Cable The power cable from the Schosche wiring kit is the big blue wire. It will have a fuse already built into the wire, my fuse was a 30 ampere fuse, but they vary depending on which kit you purchase. Start by attaching the power cable to the positive terminal on the battery. If it isn’t obvious, attach the end with the ring connector to the bolt on the terminal, which is the end of the cable closest to the fuse.
(Figure 1)
http://www.318ti.org/gallery/data/504/figure01.JPG Now comes the hard part, finding a hole in the fire wall to run the cable into the interior of the car. I used a hole by the fuse box to gain access. To do this, I used the trusty wire coat hanger method. Taking apart the interior trim under the steering wheel, I poked around until I found a hole. Then I poked the hanger up as far as it would go until it popped out of the engine bay. Then duct tape the power cable to the coat hanger, and pull it all the way through. If successful, you will have a power cable going from your battery, across to the fuse box, and through the hole.
(Figure 2)
http://www.318ti.org/gallery/data/504/figure02.jpg To gain access to the hole, you must remove the driver side knee bolster and the kick panel. The knee bolster is simple to remove. There are a few screws, easy to see, and the whole bottom of the dash simply pops off. Some of the screws may be covered with a plastic cap, which you can easily pry off with a flat head screw driver.
(Figure 3)
http://www.318ti.org/gallery/data/504/figure03.JPG The driver’s side kick panel is also very simple. There is one Phillips screw on the hood release lever, and the rest is simply held in by plastic tabs.
(Figures 4-7)
http://www.318ti.org/gallery/data/504/figure04.JPG http://www.318ti.org/gallery/data/504/figure05.JPG http://www.318ti.org/gallery/data/504/figure06.JPG http://www.318ti.org/gallery/data/504/figure07.JPG Once the trim is removed, you can pull back the carpet, exposing tons of wires. Poke around in there to find a hole to pull your cable through. Once you find your hole and get all of your cable through, burry the power cable under the carpet and move on to the next piece of trim.
(Figures 8-9)
http://www.318ti.org/gallery/data/504/figure08.JPG http://www.318ti.org/gallery/data/504/figure09.JPG Now you need to remove the door trim. This is a long thing plastic piece. It is held on by 6 small plastic clips along the door. To remove it, slide the whole piece towards the front to disengage the clips. If they don’t all slide out, you can carefully just pop it off with your hands, which is what I ended up doing. Once you remove the trim, you can easily peel the carpet back and burry the power cable.
(Figures 10-13)
http://www.318ti.org/gallery/data/504/figure10.JPG http://www.318ti.org/gallery/data/504/figure11.JPG http://www.318ti.org/gallery/data/504/figure12.JPG http://www.318ti.org/gallery/data/504/figure13.JPG Now you need to remove the rear seats. The backs fold down in the hatch, so you only need to remove the bottom part, which easily pops up just by grabbing it with your hand. They are only held on by a little metal tab on each side. Run the power cable up from the door trim and under the seat. With the seats folded down, you can easily run the cables under the carpet and into the hatch. Once in the hatch, burry the cable under the carpet and padding and have them come out on the side where the amp will be. This keeps you from having wires everywhere in the hatch.
(Figures 14-17)
http://www.318ti.org/gallery/data/504/figure14.JPG http://www.318ti.org/gallery/data/504/figure15.JPG http://www.318ti.org/gallery/data/504/figure16.JPG http://www.318ti.org/gallery/data/504/figure17.JPG Now you just need to reinstall all the trim. The seats can stay out, because you will have to remove them again when you run the next cables to the hatch. The door trim piece needs to be carefully popped into place. I ‘carefully’ popped it in with my fist. Take note of the white tabs, as they can rotate, causing them to not line up with the trim piece. The kick panel just needs the one Phillips screw and to make sure the tabs are in the right space. Make sure the tab on the top interlocks with the black under dash ceiling. The knee bolster screws back in just like it came out.
(Figures 18-19)
http://www.318ti.org/gallery/data/504/figure18.JPG http://www.318ti.org/gallery/data/504/figure19.JPG Note: On cars with non foldable rear seats (IE: not ti’s), it can be tricky getting into the trunk. To do this, you must remove the seat back and the bottom. There will be a metal firewall type wall behind the seat backs. Look around and you will probably find holes where other cables are going through. This time, however, there isn’t a huge engine in your way blocking access. Simply run any cables through to the trunk.
(Figure 20)
http://www.318ti.org/gallery/data/504/figure20.JPG RCA Cables and Remote Turn On Wire These wires run from the back of the head unit up to the amp. The remote turn on wire is the very thin blue wire. Before removing the head unit, I prefer to remove the passenger side knee bolster and glove box. With this trim removed, you can get much better access to behind the head unit and is easy to pull wires through.
To remove the glove box, you must open the glove box door. In the four corners are four Phillips screws. Some of the door components can make them kind of difficult to get the right angle. Just like the driver side bolster, there are other various Phillips screws holding it in place. Make sure you remember the one only visible with the passenger door open. When you pull the glove box out, remember to disconnect the wiring harness for the glove box light. Now the trim is completely free and you can set it aside.
(Figures 21-23)
http://www.318ti.org/gallery/data/504/figure21.JPG http://www.318ti.org/gallery/data/504/figure22.JPG http://www.318ti.org/gallery/data/504/figure23.JPG Now it is safe to remove the head unit, since you now have a place to put the wires. I don’t know how yours works, but a good place to start is to remove the face plate if it is removable. Then look for some sort of screw or tab that can be pushed to set the head unit free. Now look for the blue or the blue and white striped thin wire in the main wiring harness from the head unit. You want to connect your remote turn on wire from the wiring kit to that. You will need to strip the ends of the wires. Connect the two wires. With the glove box removed, there is now a hole where you can feed wires from the back of the head unit to the floor of the passenger seat. Pull the remote turn on wire completely through. Repeat with the RCA cables, noting which color plugged into which socket. Now you are free to reinstall the head unit, having all the wires go from behind the head unit off to the side where the glove box was.
(Figures 24-25)
http://www.318ti.org/gallery/data/504/figure24.JPG http://www.318ti.org/gallery/data/504/figure25.JPG Next on the list is the passenger kick panel. This side is a little different from the driver side. First step is to look for the rotating tab. It looks like a plastic flat head screw. Don’t let it fake you out. You will sit there forever turning it and it won’t come out. Simply turn it 90 degrees to unlock the tab.
(Figures 26-28)
http://www.318ti.org/gallery/data/504/figure26.JPG http://www.318ti.org/gallery/data/504/figure27.JPG http://www.318ti.org/gallery/data/504/figure28.JPG To remove the kick panel, wiggle it loose a little, and slide it towards the back of the car. It is simply held in by various tabs. The hardest one being the one in the middle that hooks into a hole in the metal below the 5.25” speaker. Once you remove this kick panel, you can reinstall the glove box, routing the wires right below it, but right above the black under dash ceiling. Have them go across, and down into the kick panel area where you will burry the wires under the carpet.
(Figures 29-31)
http://www.318ti.org/gallery/data/504/figure29.JPG http://www.318ti.org/gallery/data/504/figure30.JPG http://www.318ti.org/gallery/data/504/figure31.JPG Now just remove the passenger side door trim and burry the cables along the carpet. This is the same as the driver side. Run them up under the rear seats, and into the hatch. Once in the hatch, burry the cables under the carpet and padding and have them come out on the side where the amp will be. This keeps you from having wires everywhere in the hatch.
(Figure 32)
http://www.318ti.org/gallery/data/504/figure32.JPG Reinstall the rear seats. This is easy; all the need is a pop with the fist to make them lock into place. The door trim is the same as before. The kick panel can be difficult with all the tabs. The hardest one is the one in the middle that you have to hook into the metal hole. After some wiggling around, you should be able to get it right. Once installed, there is some black trim that should be over the edge of the kick panel. You may have to go around and pry it out with a tiny flat head screw driver.
(Figures 33-34)
http://www.318ti.org/gallery/data/504/figure33.JPG http://www.318ti.org/gallery/data/504/figure34.JPG Finishing Up If you have made it this far, you should have the entire interior put back together, with all the wires in the hatch area. Now all that is left is to ground the amp and hook up the other wires in the hatch.
To ground the amp, you want to peel back the carpet and expose the metal body of the car. Take the ground cable, which should have a ring connector on one end, and screw it into the metal with a sharp tipped screw and a washer to hold it in place. Connect the other end to the appropriate place on the amp.
(Figure 35)
http://www.318ti.org/gallery/data/504/figure35.JPG Once it is grounded, go ahead and connect the other cables and plug in the RCA’s. Using speaker wire, connect the amp to the sub box in the appropriate place.
Make sure you connect everything to the right place. The amp will be labeled. If you mix up the ground and power cables, you will most likely blow a fuse. Make sure the right color RCA is plugged in the right socket. Lastly, make sure the speaker wire terminals match up (positive to positive, negative to negative).
Once you are certain all the wiring is complete, reconnect the battery and crank that baby up!
(Figures 36-37)
http://www.318ti.org/gallery/data/504/figure36.JPG http://www.318ti.org/gallery/data/504/figure37.JPG IMPORTANT NOTE You can burry any excess cable under the hatch or trunk carpet/padding. This way you don't have wires everywhere in the back. However, make sure you provide enough slack as subs will slide around some. The first day mine were installed, my RCA cables didn't have enough slack. My friend wanted to check them out, pulled on the box a little, and the plugs snapped off, leaving me with no RCA plugs at my amp. Luckily, my pops is an electrical engineer and he soldered new RCA plugs on the end of the wire, but if you don't know how to do that, you will have to rip your car apart and run a new set of cables!
Trouble Shooting If there is no sound coming from the subs, you should first check to make sure the amp is powered. There should be an indicator LED on it somewhere that will light up if it has power. If the amp is not powered, then it could be a blown fuse, an issue with the power cable, or a problem with the remote turn on wire. Also make sure that the head unit is powered on. If the head unit is off, the amp will be to.
If the amp is powered, but still no sound, check the amp settings. I spent 2 hours my first installation trying to find the source of failure, when it was simply that the bass gain was set to 0 as a default from the manufacturer.
Lastly, double check your RCA cables and speaker wire. Make sure you didn’t plug them into the auxiliary input of your head unit, if your head unit has that. Make sure the right colors match up to the right sockets. Make sure the same side of the speaker wire goes from positive to positive and negative to negative.
Installing Subwoofers 
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