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Installing Subwoofers
Installing Subwoofers
How I Installed My Subs In My 1995 318ti
Published by robcarync
Default Installing Subwoofers

Sub and Amp Installation in 1995 BMW 318ti


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 friendís 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)


Now it is my time for my personal rant. Some kids my age just donít care about looks and donít 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 didnít 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 isnít 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)


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)


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)


The driverís 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)





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)



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 donít 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)





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)





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 Ďcarefullyí 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)



Note: On cars with non foldable rear seats (IE: not tiís), 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 isnít a huge engine in your way blocking access. Simply run any cables through to the trunk.

(Figure 20)


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)




Now it is safe to remove the head unit, since you now have a place to put the wires. I donít 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)



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. Donít let it fake you out. You will sit there forever turning it and it wonít come out. Simply turn it 90 degrees to unlock the tab.

(Figures 26-28)




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 5.25Ē 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)




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)


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)



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)


Once it is grounded, go ahead and connect the other cables and plug in the RCAís. 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)




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 didnít 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.
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By red96ti on 09-30-2006, 07:31 AM
Default running wire through firewall

I just wanted additional details of how you thread the wire through the firewall. Photos would be great. (I checked other threads without getting the info I needed).

I have found where it appears where I can sneak the wire through along the factory car wiring behind the pedal cluster, however, I cannot easily see where it pops out in the engine compartment.

Is it easier to work if I remove or loosen the fuse box?

(this is a US spec car with left hand drive... so fuse box is on driver's side and batt on pass side)

Thanks in advance.

Before I drill any holes, I just wanted to be sure I am trying the right things.

Might sound also like a silly question -- but does anyone ever run wire *under* a car and pop the wire up through the spare tire access area in back?
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By robcarync on 09-30-2006, 02:46 PM

I did not drill any holese at all. I used the trusty wire coat hanger method. My pops stood by the fuse box area, and I poked around with the wire hanger through the hole by the pedals. Eventually it popped up (the hole is pretty far down there. You may need to bend the hanger so it kind of hooks upwards.) Then we duct taped the power cable to the hanger and pulled it through from the insdie.
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By red96ti on 10-08-2006, 09:42 AM
Default got the wire through

Thanks for the tutorial and the clarification.

I finally found a place I could squeeze the wire through the firewall in an existing grommet behind the pedals. I think a braided cloth fluid line passes through this grommet... possibly clutch or brake fluid line? I just squeezed in the 8 ga. wire next to it but made sure it wouldn't crowd out the fluid hose.

Where this pokes through into the engine compartment is about 8 inches below the top of the fuse box (a guesstimate, I didn't measure it) and to the left a bit (towards the pass side slightly).

I was going to snap a pic, but it is one of those things that'd be impossible to see, as I sort of had to squeeze in my head sideways to see what I was doing.
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By ConMasta on 12-03-2006, 01:03 AM
Default Existing hole on firewall...

Just to let you know, that existing hole behind the pedals will be ridiculously difficult to fit 4ga through. It took me and my sister about an hour to run the length of the power cable through it. The from behind the pedals enters a little box area and at the top of that box area there is a tiny exit hole facing upwards; that hole is located under the brake booster cylinder, tofind it, shine a light thru the hole behind the pedals and look in the engine compartment.

Its hell fitting 4ga thru both holes because it snags, the upper hole is barely large enough so that you must feed/pull at the same time, requiring 2 ppl.

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By Keach on 12-03-2006, 07:33 AM
Default Hole in firewall

Hey guys when I put my subs in a while ago, I found a hole in the firewall behind the battery case. Its a small pain but if you remove your battery and take out the battery tray there is a rubber hole for running wires. I used a standard screwdriver with the sub wire taped to the end of it running parellel. Shouldn't be too much of a problem from there. Then I ran the wires under the passenger side carpet and under the trim all the way to the back. It only takes a second to pull up the back seat and run them under it. Not sure if you guys are using the same entry point in the firewall, but the one I used I would really recommend. It's worth the time to take out the battery and the case and you can't miss the hole after you do so. Toughest part for me was getting the trim to stay back on with the wires under it, but it all worked out and no wires are visable at all. Good luck guys and remember keep it lookin clean!
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By robcarync on 12-14-2006, 03:27 PM

I was able to fit a power cable through the hole I mentioned without much difficulty, but I did have my pops helping me so it made things simpler. The only issue that could be seen with running the power cable down the passenger side is that in good form, the power cable should be ran down the oppisate side of the car as the RCA and remote turn on cables. This is to prevent possible interference. I have never tried running the cables together, so I don't know if you will get any feed back or interference, but it is something to think about.
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By aznlonewolf135 on 01-27-2007, 03:28 AM

I don't know about you guys...but it took me forever to find the hole...and tread it...I made a small fish eye at the end of the hanger and feed it down from the hood and snaged it from the inside...

I found the hole by sticking a flash light in it and finding where the light comes from on the other side.
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By robcarync on 03-08-2007, 10:34 PM

Yes, finding the hole is tough. That was the hardest part for me. I used a flashlight and a coat hanger too.
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By sixafterfour on 06-13-2007, 09:45 AM

oh god, it was a 2 hour ordeal.
okay you have that large bundle of wires and with a coat hangar you will get into the fusebox, You DONT want to use that one, it wont even fun
However about 3" to the right under a little bit of the foam a hole that will just do fine
man what a pain.
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By classicronnie on 12-02-2007, 08:11 PM

can someone take a picture of where the hole to run the power cable is???
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By classicronnie on 12-03-2007, 12:11 AM

aight put it throught the fuse boxx, subs sound way better in the hatch than my old jeep
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By 2cam16 on 12-03-2007, 03:48 AM

Originally Posted by classicronnie View Post
can someone take a picture of where the hole to run the power cable is???
It's not a hole. It's a rubber grommet in the firewall right below the battery box. Remove the battery and you will see it there. Pretty easy.
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By classicronnie on 12-03-2007, 05:02 AM

i ran mine through the fuse box fool
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By lpossie on 04-05-2009, 08:38 AM

First of all, thx for the tutorial. It was exactly what I needed!

I managed to get everything installed, but I'm having issues trying to get my amp to turn on. I have a Alpine MRA-F350 amp. I have secured the battery cable to the positive post on my battery and placed it on the battery terminal on my amp. The amp is grounded as well. The only thing I can think of is that the remote turn on is not connected correctly. I'm still using the stock amp that came with my 318ti, so I have the stock amp, the new sub amp all connected to the blue/white cable on the head unit harness. Would this be my issue? Has anyone else ran into this problem before? Any suggestions? Thx!
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