This guide has been sourced from pug306.net I have put it on this site with the owners permission. This is a very good guide and should help you to do everything you need. This was written by Chapperz.
This is specific to wiring up a JBL 10" 1000W subwoofer and JBL GTO 6000 (1100 W) amplifier with no ready bought kit, to a 5 door phase 3 - many things will vary depending on the subwoofer and amplifier you use, and the type of 306 you have, but I'll try and state in the guide what these things are.
First stage - get all the bits you need
1 x Subwoofer (JBL 1000W)
1 x Amplifier (JBL GTO 6000)
1 x AGU Fuse Holder (http://www.a1caraudio.co.uk/dynamics-fh20-...der-p-5567.html)
1 x AGU 60A Fuse (http://www.a1caraudio.co.uk/dynamics-fuses-p-5561.html) [AMPAGE WILL DIFFER DEPENDING ON WATTAGE OF AMPLIFIER]
1 x Power Cable (8mm) [SIZE WILL DIFFER DEPENDING ON WATTAGE OF AMPLIFIER]
1 x Audio Cable (Between 6 - 6.5 metres long)
1 x Remote Lead
2 x Yellow RCA Plugs
2 x Red RCA Plugs
2 x Black RCA Plugs
2 x Ring Terminals
1 x Rubber Grommet [SIZE WILL DIFFER DEPENDING ON SIZE OF POWER CABLE USED]
1 x Real of insulation tape
1 x Short length of ‘figure of 8’ speaker cable
Second Stage - running the power cable to the rear of the car
All the wiring will be down the passenger side of the car.
I'm running the power cable from the front to the rear of the car, but it doesn't matter if you do it from back to front, as long as you leave yourself enough length at the front to go through into the engine bay.
Underneath the glove box, in the passenger footwell, you'll find a cover attached to a metal bar with three clips on. Pull these clips off the bar and the cover should come of nice and easy:
Pull up the rubber door seal at the bottom of the door and pull the carpet to the side:
Thread the power cable under both the carpet and the yellow foam up to the top of the footwell:
Now thread the cable down the side towards the rear of the car, along with the other cables which should be there, pulling the carpet to one side as you go:
You will find that the plastic cover over the seat belt mechanism prevents you from pulling the carpet aside. Therefore you need to remove the screws in the holes shown below (using a torx screwdriver) and pull the cover to the side (no need to remove cover completely). You will probably need to slide the passenger seat forwards fully.
You will now find that you can't continue running the cable along down the side because of the block where the passenger seat slider mechanism is located:
So you'll need to run it round the block, but still under the carpet. It's a little tricky, but just requires a bit of awkward hand positioning.
Now you'll need to remove the rubber door seal from the rear passenger side and pull the carpet to one side, just like on the front door. Continue to slot the cable in along the side between the bodywork and yellow foam, and bring the cable up by the rear seats. Now simply slide the cable under the seat and into the boot. I've taken it along to the opposite side of the car and up, because my amplifier will be on the driver’s side.
Third Stage - running the audio cable and remote lead to the front of the car
First of all, use your insulating tape to bind the two cables together - simply wrap some tape around both wires every 300mm or so, as shown below:
Now run the cable down the exact route where the power cable now runs, all the way to the top of the passenger foot well.
I'm running these two cables from the rear to the front of the car, but it doesn't matter if you do it from front to back, as long as you leave yourself enough length to get up to the head unit.
Fourth Stage - drilling hole into engine bay for power cable
We now need to drill through from the foot well into the engine bay, so the power cable can be attached to the battery. It's much easier to drill from the foot well rather than the other way around.
Ideally, we want to drill through somewhere in the red circle below:
Which, when you look in the foot well, comes to roughly here:
Now drill the hole - start with a pilot hole, then use a drill bit with diameter just bigger than the power cable:
De-burr the sharp edges of the hole and slide the rubber grommet onto the end of the power cable, before pushing the cable through into the engine bay and pushing the grommet onto the hole. If the cable runs through the grommet too easily, just wrap a bit of insulation tape around the cable where it goes through the grommet:
Now just pull the cable up and round the ECU box and battery box, tucking it in to make it look neat where you want, and just leave it there for the moment.
Fifth Stage - connecting the audio cable and remote cable to the back of the head unit
Using a torx screwdriver, remove the below screw to allow you to reach up under the panel:
Now remove your head unit, so that it looks something like this:
Now for the tricky bit. You need to thread the two cables up behind the panel where you've taken the screw out, up to where the head unit is located. You can take the whole centre dash off, but it's possible and much less hassle to do it without and instead just push the cable up behind the dash until it pokes out at the top.
Once done, you might have some cable spare so cut off any excess, making sure you have enough to go to the back of the head unit. You'll also have a lot of loose ends of cable - this is where the RCA plugs come in.
Strip the end of each cable so they look like this:
Un-screw each RCA plug so they look like this:
Now you will need to solder each wire to each hole:
As you can see, the wire without any coloured coating goes through the hole on the big gold platform, and the coloured coated wire goes through the smaller hole. You can then solder the wires in place and screw the plug back together. (Make sure you slide the top half of the plug up the wire before soldering).
You should now have two red plugs attached to the cables with red coating on the wire as shown above, the two yellow plugs to yellow and the two black plugs to the white coated wires.
You don't need to attach an RCA plug to the remote lead.
You should find a small blue box somewhere amongst the wires, with a blue and white wire already running through it. Open this up, place the end of the remote lead (once stripped) against the metal (in the slot) and close it back up. I don’t like these little connector boxes and have chosen to use a crimp instead, which is why my blue bit will look different to yours – but it does the same job.
You can now replace the head unit and screw the panel back on.
Sixth Stage - connecting all cables to subwoofer and amplifier
Do not plug in the RCA Leads until last of all. This is to prevent the earth tracking being blown in your head unit.
You will need an earth for the amp too. So cut a new bit of cable out of the spare power cable you have, strip both ends and attach a ring terminal to one end:
Now undo one of the bolts in the very back of the boot, put the ring terminal over the bolt and screw it back into place.
You can now screw the other end of the cable into place on the amp (should be labelled 'GND'). While your there, you can also screw the power cable ('+12V') and the remote lead ('REM') into place. (I have put red tape round the power cable to show it's live and black around the earth - normally the power cable is coloured red anyway):
You'll need a new bit of standard ‘figure of 8’ speaker cable to go between the sub and the amp now, so cut it to length, strip both ends, and connect up as shown:
Final stages - connecting power cable to battery, attaching RCA Leads
Drill a hole into the battery casing where you want the top screw located, then do the same at the bottom before screwing the fuse holder into position:
Get the end of the power cable and strip a little of the plastic back:
Insert the end into the right hand side of the fuse holder:
Get another spare bit of power cable, strip one end of that, and insert it into the opposite end of the fuse holder:
Now strip the other end of the cable and attach the other ring terminal to it:
And attach it to the +ive on the battery:
Now insert the fuse into the holder and replace the cover.
Now you can set up your RCA cables!
And you’re done!!!
To hold my amp in place, I've placed some plywood under the carpet, just bigger than the amp, and then screwed the amp threw the carpet into the wood.