This guide was taken from cavweb-forums.co.uk and was written by PSX
I did this in my 1995 N reg Cavalier 1.8 LSi. I believe the procedure described will apply to many other early/mid 90s vauxhalls, but be aware that they may not, and to refer to your Haynes manual to double check. Read through this whole article before you start, in case there's something you missed! I accept no responsibility for any damage caused through the actions outlined here, but I have made every effort to explain where caution is necessary. Send any questions via private message or reply here.
1. Tools required: 10mm spanner (or as appropriate for disconnecting battery leads), medium sized philips (crosshead) screwdriver for removing various trim panels, medium sized flathead screwdriver (undoing trim panel clips from inside footwells), LARGE flathead screwdriver (leverage under footwell side trim panels), pliers (pulling wire through firewall), head unit removal tools, cutting knife (cutting into firewall wiring hole grommet) - stanley or swiss army will do fine, paint removal sandpaper (making a good earth connection).
You may also need a drill to make a new hole for securing the earth lead later. You may also need a rubber grommet if you need to drill a second hole through the firewall to run your power cable, to prevent water entering the passenger footwell.
A torch will help if you are working in bad light.
2. Kit required: Amplifier, speakers/subwoofer (if you buy a subwoofer, you'll need to buy a subwoofer box to mount it in). Autoleads wiring kit - appropriate for YOUR amplifier (for this, you should refer to the MAX watts on your amp. If the amp has a MAX number above 360w, then don't buy the autoleads kit meant for UP TO 360w. This is important, because regardless of the fuse used, you will just overheat the wires if too much current is being supplied through them). If you choose to buy the wires separately, you will need: 5m power cable (with fuseholder in-line), 1m earth cable, 5m remote turn on lead (so head unit will turn amp on/off), 5m male-male phono leads (shielded if possible), correct fuses (recommend buying a 10a, 20a and 30a set just in case). You will also need to make sure that the earth, remote turn on and power cables have proper terminals fitted - small ones for the amp end, larger ones for the battery (power) and body (earth) ends. You will need a largeish self-tapping screw to earth to the existing hole in the boot, or a smaller one if you drill the hole yourself.
You may find that shorter leads are ideal if you are fitting in a Corsa or Astra. I found that 5 metres was a perfect length for the Cavalier. Bear in mind that your wires will need to be routed round some corners and behind the dash when measuring - having some slack is not the end of the world!
NOTE: The earth and power wires should be thicker, the more power you plan on running through them. Here is a table showing which thicknesses are appropriate (bear in mind that the wattages used here are RMS rather than MAX, so check what the RMS output is for your amplifier first):
NOTE 2: Your head unit must have a means of delivering output to your amplifier. Most modern head units have what is called an RCA or phono output - 2 phono plugs, left and right, which is ideal. I believe some other head units have a high level output, but some may not have either. Check that your amp accepts high level input if your head unit only has a high level output.
NOTE 3: Take care that your amp is not vastly overpowered in comparison to what your new subwoofer/speakers can handle. With the correct setup, you can run any subwoofer/speakers off any amp, but it will be easier to blow the subwoofer/speakers if the amp is too powerful. Choose a subwoofer/speakers with a RATED value that is equal to or higher than the amplifier's RMS, if possible. This means that it will be very difficult to blow the speakers with that amp. (The MAX figure for speakers is essentially the amount of power they could take without self-destructing. The RATED figure is the maximum amount of power they are designed to operate at constantly. Exceed this and you risk blowing the speaker coils).
3. Let's get started! Ensure the ignition is OFF, clear enough space around the car for all 4 doors to be opened, secure the car with handbrake and engage 1st/reverse gear if you are working on a hill to make doubly sure. Open the bonnet, and with your 10mm spanner carefully undo the negative lead (should be closest to the passenger side of the car, and with a connection straight to the body of the car) from your battery and place the lead away from the terminal.
Now climb into the footwell of the passenger side of the car and look up underneath the glovebox. You should see some black plastic trim secured with 4 plastic turnclips:
You can use your medium sized flathead screwdriver or your fingers to undo these but take care you do not turn them the wrong way, as they are broken with brute force. I believe you turn to the right (clockwise) to undo them. Remove the trim panel and place it in a rear passenger footwell til later. Now sit in the passenger seat and open the glovebox. Remove everything from the oddments tray above the glovebox and the glovebox itself, including the rubber mats. Now look just inside the oddments tray to the left and right sides - you will see some 5x4cm (approx) plastic clips that can be levered out from the bottom with a screwdriver. Take both these out. Now reach inside the glovebox and push the screwdriver blade up on the right or left hand side behind the oddments tray. Apply leverage with the screwdriver and pull back with a large amount of force on the oddments tray - it will suddenly give a loud pop and come out. It is secured by 2 large plastic clips which seem difficult to break, so simply pull harder until the tray comes out.
Gently prise out the front of the glovebox light from the right hand side of the glovebox and remove the connector (black wire will be uppermost when you come to refit). Place the light in the centre console oddments tray for safekeeping, and push the wiring lead for the light back through the hole in the glovebox. With the glovebox still open, look for 4 securing screws at each corner. The lower screws are fiddly to access - try partially closing the lid if it helps access. Remove all 4 screws, then withdraw the glovebox and place it on one of the back seats.
You will now have a great view through to the firewall. Look at the upper left hand side (you may need to get back down into the footwell to see) and you should see the main wiring bundle passing out through a large hole (approx 3cm diameter). With any luck, this hole will be large enough to push your power cable through. If not, you will need to drill a second hole and place a rubber grommet in the hole to prevent water coming through. If you do drill a hole, take care not to pierce any other cables/pipes that may be running through the engine bay.
Find your power lead with in-line fuseholder, and REMOVE the fuse from the holder. Holding the end of the power lead closest to the fuseholder, undo one bolt on the positive terminal of the battery (not the one which secures the lead itself) and connect the power lead here. Make sure the bolt is fairly tight. Route the power lead in a sensible fashion back through your engine bay, making sure it won't fly towards any moving parts or hot pipes later.
NOTE: this photo was taken AFTER the install was completed - your battery negative lead should still be disconnected!
If you are pushing your cable through the existing grommet and hole (like I did), do it from the engine bay side. Find your knife, and make a reasonably big cut, TAKING EXTREME CAUTION not to cut any of the existing wires! (the rubber is stiff). Twist the blade a little to help widen the hole. Looking in from the passenger side of the engine bay, I made the cut on the upper right hand side. Taking care not to break off the terminal from the cable, firmly push the wire in a fair way (5cms or so) and then climb back in the passenger footwell to pull the end of the wire through the hole, and continue pulling it through until it is all the way in the footwell. Check that the cable is still routed as you want it through the engine bay, and the slack is pulled through properly. If the hole in the grommet was particularly large, water could seep in here, so seal the grommet again with paste or tape of some sort.
4. This step involves running your power lead and remote turn-on lead back along the passenger side of the car through to the boot. (It is important that the power leads run on the OPPOSITE side of the car to your phono leads to prevent cross-talk and distortion, so don't try and cheat by running them all down this side!) Using your medium flathead screwdriver, pull out the plastic clip securing the front left quarter trim panel nearest the floor. Pull back the grey (stiff) rubber weatherstrip to allow you to pull this panel out to the right a little, and then more so by pulling from the back (nearest the engine).
Make all efforts to get your fingers underneath the top doorstep panel on its top edge, not near the carpet, and tug on it with moderate force to get an idea of how tightly these buggers are fixed in! There was no glue or screws holding these in my car - just plastic clips. They are quite tough though, so as long as you aren't bending the panel TOO much, don't worry. Look for small dots in the plastic on the outside, near the carpet. These indicate where the clips are located:
Pull UPWARDS near each of these dots, using your large flathead screwdriver for a bit of leverage if necessary (watch that you do not break the existing wires if you do this). With a lot of force, these clips will eventually pop out with large pops each time. Open the left hand rear passenger door too, and pull the panel up here too, starting from nearest the seat. Finally, pull the panel away left and right of where the front passenger seatbelt mounts at the floor, and with any luck you will have freed the entire panel!
The existing wiring runs along this channel secured by plastic tags. Feed your power cable around one of the existing wiring bundles from where you went through the grommet, down to the left, and then down behind the front quarter trim panel and through to the doorstep channel where you were just working. Feed the wire through each plastic tag until you reach the rear passenger seat. Now you have two choices - you can try and make the wire very discreet by running directly backwards under the trim panel, (generating more work for yourself, which I will not cover here), or you can go beside the rear passenger lower seatbelt mount and up behind and then between the lower and back of the seats into the boot, like I did:
Make sure the cable is not within interference range of any hinges, and that the seat still comes down properly with normal pressure when released.
Now find your remote turn-on lead in the wiring bundle from your head unit, and if necessary, remove the head unit to get better access to the wiring. Find the remote-turn on connector from the wiring bundle on the head unit and connect it to the remote turn-on lead. If your wiring kit is anything like mine, you'll find that the connector already fitted to the wire is no good, so pull it off with pliers gently, leaving you with bare wire. Run this wire around one of the other spade connectors provided in the Autoleads kit so it's fairly secure and connect it appropriately. You may choose to solder the connection instead, or simply twist the wires together and use tape to insulate it. The choice is yours - this connection does not need to be 100% perfect, but it shouldn't come apart, since then your amp won't know when to turn on/off.
NOTE: If you don't have a remote turn-on lead, you'll need to make your own switch, and fit it somewhere convenient (probably inside the glovebox, as a first suggestion).
Feed the remote turn-on wire up around the wiring bundle that passes next to the black plastic air ducting that goes to the passenger air vent. Take the wire down to meet the power cable, following an existing cable bundle if possible, and run it along through the plastic table tags in the doorstep channel, to the back seat, and through them as you did with the power cable, to the boot.
5. We're halfway done! I recommend NOT refitting the doorstep trim panel yet, since there could be a problem with the wiring later. First, look up inside the driver's side footwell and undo the clips supporting the black trim panel as you did under the glovebox. Place the trim panel out of the way. Look for the bonnet release handle on the right hand side - pull it carefully towards you and (in theory) it will just pop out. Mine has a tendency to come out ALL the time when pulled from the wrong angle, so getting it out was not an issue for me. Yours may be glued in, so you might need to take the torch and have a good look before you try to take it out. Once it's out of its lughole in the metal, pull it upwards and over to the right, out of the way of the front right quarter plastic trim panel. Use your medium flathead screwdriver to pull this clip out as you did with the driver's side, and jostle the panel from the back so that you have access down the side.
Open the fusebox flap, and locate the 4 screws (2 upper, 2 lower).
Undo them all with your Philips screwdriver and this whole plastic panel, which goes right across under the steering wheel, will now hang down on the right side. It unclips easily from the left. Take it off and place it out of the way. Now pull the bottom of the fusebox gently so it pops out, and pull the box unit down slighly so the plastic clears the dash and you can get your arm up behind the fusebox.
Now for the phono leads. Working from the passenger's seat, remove your head unit and disconnect it from the wiring bundle. Feed your phono leads through the head unit's hole and with your arm moving through from where the glovebox was, take the wire through from behind the head unit and push it towards the driver's side of the car, keeping your arm straight. Put your other arm through the gap under the steering wheel left by the panel with the fusebox flap. Feel around up on the left with your right arm, whilst pushing the cable through with your left arm, eventually you should feel the phono plugs with your right arm and you can pull them through gently. Feed the wire carefully down and lay it along the black plastic air ducting just inside and below the hole left by the fusebox cover panel. The wire will need to go up again before you reach the fusebox, so put your right arm up behind the fusebox and again find a spot for the phonos to pass through from the left. Guide them through, and then pass them down towards the existing wire bundles running behind the front right footwell quarter trim panel.
Now remove the doorstep trim panel as you did on the passenger side of the car. There will be fewer wires this time, so you should easily have room to route the thicker phono wires through. Take the wires between the seats as you did on the opposite side of the car, to the boot. Reconnect your head unit and plug in the phono leads (Red to Red (Right), black to Left (white)).
6. Nearly done now! It is important that we create a strong earth connection for the entire setup. A short could blow the fuse in the amp or on the power lead. Lift up the boot carpet from inside the back of the car, and you should see 2 plastic plugs that almost match in with the colour of the metal - one towards the left side of the car, the other to the right. Pull out one of the plugs, and you will find a hole (largeish) that is perfect for earthing your amp to. You may find (like I did) that you have no self-tapping screws large enough for this hole, so drill a smaller hole slightly further towards the driver's side of the car for one that you do have, and one that is not too big for the earth terminal. See photo:
Use the paint removal sandpaper to remove the paint until you reach shiny silver metal in a wide enough circle for all of the earth terminal to sit in, and fit the terminal with the screw turned tight. Once you've checked that the setup is working properly, you should paint over where you sanded to prevent rusting. Painting over the terminal and screw too is fine.
7. All the hard work is done! Connect up your speakers, your power cable and earth cable to the amplifier, and turn the gain knob down to its minimum. Not sure which polarity the cables are for your speakers? No problem! Take a standard 1.5v AA battery, and connect one wire of the speaker to the positive end of the battery, and the other to the negative (this procedure is fine for subwoofers too). If the speaker moves OUT (up towards you) then you have the POSITIVE wire connected to the POSITIVE terminal of the battery. If the speaker moves IN (down back into the speaker) then you have the NEGATIVE wire connected to the POSITIVE terminal of the battery.
Now go back to the engine bay, and CAREFULLY reconnect the negative terminal to your battery (it WILL spark, so take care!).
ONLY NOW should you be considering putting a fuse into the power cable! Check the fuse installed in the amplifier, and take one of the same rating and push it into the fuseholder on the power cable, taking care not to touch any metal on the fuse or inside the holder. Go to the back of the car and check that everything seems ok and that there's no smoke! If you do see smoke - which is highly unlikely - disconnect the battery negative terminal quickly and check everything over again.
And finally, the big switch-on... Turn on your ignition and head-unit and again, make sure nothing is smoking. Go to look at the amplifier and you should see its power light on. If all is good so far, everything is most likely present and correct! You can test the subwoofer now, but leave adjustments til later when all the trim is back in place. Check that when you turn the ignition off, the amplifier turns off too - otherwise your battery will be flat in the morning!
Congratulations on installing your subwoofer and amplifier! Pulling out trim panels can be daunting but now you've done it, you should feel more confident working around the car in future and of course - installing more audio systems if the need arises. Make sure that you securely mount the amp - either on its side or face up, but NOT upside down, since this will just mean that heat cannot escape from the amp. Screwing into the carpet should be fine, as long as the carpet won't fold over and turn upside down whilst driving. Also securely mount the subwoofer box, with velcro or screws, since even the heaviest of boxes will slide around in tight turns!
Refit all trim panels in the same order that they came out, pushing the doorstep trim panels firmly into place and pushing the seatbelt out of the way when refitting at the centres. Push your bonnet release handle back over to the left of the front quarter footwell trim panel before you refit it, and check that both these panels go back properly and do not shift from left to right at the front ends. Also make sure that in the driver's footwell, the black trim panel that you took out first is securely hooked with the clips, as if it falls down while driving it could get in the way of the pedals.
Ensure that you pull the wiring for the glovebox light back through the hole in the glovebox before you push it all the way in and remember that the black wire should be uppermost when the light goes back in its socket.
Double check that your battery connections are tight before you shut the bonnet, and you're done!
Here are some photos of my completed install:
http://www.btinternet.com/~psx10/cav..._installed.jpg
http://www.btinternet.com/~psx10/cav...oofer_boot.jpg
http://www.btinternet.com/~psx10/cav...ofer_boot2.jpg