It started with a cranky faulty HU (Head Unit) and the MP3 player could not play. Quickly replaced it with Double Din HU. Out comes the climate control panel and all the cable and electrical clips. If you are doing this yourself , go slow and undo the clips and be patient. Access to the old HU will be possible. Only 2 screws holds the HU in place. New brackets were made for the Double Din HU. The matching wire HG harness was soldered to enable the quick release feature for future retrieval.
Top is supplied with HU purchase
Bottom harness is connected to factory wire harness
The old stereo and pocket to keep rubbish
Be prepared for many trial and error fitting with the custom brackets. Fit in the new HU and reuse the old screws to secure it in place.
Poor man's helper hands to solder the two together. I don't like to cut off the factory wiring.
Soldered wire
Completed new wire harness
Clip in the new harness, original factory
wires are not cut
Fit in the new HU
and reuse the self tapping screws
AMPLIFIER 4 SPEAKER CROSS OVER INSTALLATION
Not too long later, the rear oval shaped factory speaker surround material that holds the cone disintegrated and the speakers sounded terrible. Out goes the old ones held on by just 4 screws. But the new ones are 6.5 inch round ones so an adapter plate is required for a successful mount. I 3D printed one and was happy with the results. Soon it failed and wrapped under the sun so i made 1.2mm thick aluminum sheet. This was CNC cut out to reduce distortion.
Blue color plastic 3D print. Wrapped under the sun.
CNC machined out. No wrapping
Perfectly aligned holes and curvature
Dry fit. Looks damn good
WIRE INSTALLATION
The nightmare is about to start. 2 wires for rear speakers, 2 wires for front speakers, 4 RCA for the 4 channels and one big wire for the power to the amplifier. One more wire to REM
REAR WIRES
The rear seats , all cosmetic covers in the trunk and cabin areas were removed to make way for the wire layout. Rear wires were easy but they need to tuck under the floor carpet for aesthetic reasons. I use laundry lines to help thread the wires through. 
Green leader line leads the way
Tape the speaker wires and pull through.
Tape together with factory wires and make sure the wires clear the cosmetic cover's snap clips
This one was tough. There's no way into the cabin from the door and the factory makes dedicated plugs with rubber boots to keep out the water. Many would thread the speaker's wire here. But using 16 Awg wire for me just wouldn't work. I starred at the problem for a good 45minutes before i saw the solution. Its not made known to the public but the manufacturer made a square opening at the hinge pin that leads back to the cabin. Water is not able to get in because of the door's weather rubber strip. Here's the chance. Its a tight squeeze for the speaker wires as well as the tweeter wires. Rubber grommets were use to prevent the sharp chasis from cutting the wires.
That's the only hole back to the cabin.
Center console was removed to make way for the wire on the right speaker to travel back to the amp. 
So the last piece of wire, the power cable, must be connected to the battery and goes into the cabin area and connect back to the amp.
BATTERY POWER CABLE
I looked for existing grommet that the factory has left behind so that I can fit the 4AWG wire past the firewall but there isn't one. Finally there was just one but at the left hand side of the car just before the A pillar.
Fenders and mud guards were removed to route this thick wire in. Get the quality flexible multi strand wires to make the job easier.
Remove fender and headlights
Power cable zip tied for safety
From cabin out to battery terminal
Terminate the wires with quality copper sleeves, crimped spade connector and 60A fuse box.
Spade connector to +ve battery end
More than 200 strands of fine copper and flexible rubber insulator.
Copper sleeve and solder added
Bad ass 60A fuse box added
REM WIRE
This is the wire that turns on the Amp when the HU is activated. It sends +12v to AMP remote turn on terminal. Its like a switch but controlled by the HU.
Quality thick sponge
Its a small wire so i use a small connector and added another copper sleeve for assurance.
TERMINATING SPEAKER WIRES
To get the best sound and years of trouble free stereo, use proper connector. Here proper crimping technique is also applied.
Spade connector and insulating sleeve. Cross over tweeter wires connected as well
I zip tied the adjacent wires so that it wont come off easily.
Black remote turn on wire in the background. The rest are speaker wires with proper crimped terminals
This power cable is dangerous hence the added bellows for more protection
Multi strand speaker cable. Very high quality but no brand.
PUT IT ALTOGETHER
The front speakers are mounted using the plastic bracket that came with the purchase and they worked fine. All wires are neatly tucked under the carpet and arranged.
Front Left
Front Right
FRONT SPEAKER BAFFLES
Water can sip through the window areas. You need this one so that front speakers will not have water damages. ABS 3D printed these and fits in exactly. ABS will withstand summer temperature and hold its shape.
Front view of water baffle
Side view of Water baffle
AMPLIFIER FLOATING MOUNT
Most installer will secure the Amp either behind the trunk or put it under the front passenger seat. Trunk space are precious and will need longer power cables and add up cost. Put it under the passenger seat means it might be kicked by rear passengers and also reduce leg room. The idle mount is a floating Amp. Brackets are made and bolted to the seat and the Amp mounted to this bracket.
Bracket and MDF board assembled
12mm MDF board used for strength and seperate chasis GND from Amp
Checked the chair sliding clearance when it moves forward and backwards
GROUND WIRE
This wire is anchored to the chair itself since its all metal underneath so doing it this way means rear passengers will not kick onto it.
The Ground wire for the Amp. Its a strong connection point
TWEETER SPEAKER
i dont like cutting the factory door interior panel to install the tweeters so i made a curved triangular box and it sits on the dashboard top. Easy.
Add a badge and it looks awesome!
POWER UP
Connect all the wires to the amp and turn it on. The amp lights up and the music fills the interior. Sound imaging is great and seems to come directly at you in front of the car. Just amazing!
COMMON PROBLEMS
The trunk torsion bars are going to vibrate once the volume is cranked up. Simplest fix is to pack in between these bars with thick sponge and damp the annoying resonance.
Damping the torsion bar vibration
Waterproof rubber baffles for the rear speakers and the thick sponge to dampen the vibrations
CONCLUSION
This DIY project is not for the faint hearted. It involves a lot of foresight and identifying problems. If you are not comfortable doing this yourself, pay someone to do it before you damage the vehicle as it involves a lot of wiring and dismantling of cosmetic panels.
