So as I've done with almost all of my cars I'm swapping the sound system of my x-trail t31 (diesel).
I divided this project to three major steps so that after each step audio system is fully functional and I can prepare for the next step (gather know-how and purchasing equipment).
1
So my first step was to install external AMP.
I selected refurbished MAC Fearless 5000D. It's a 5 channel amp and it will power the whole system.
Idea is to keep stock HU and speakers for now, add amp and sub-woofer only. To make this work, I have to re-wire everything.
So first mission was to run power wires (I used 2 parallel wires because I had them left over from another project and it seemed unreasonable to buy one thick wire. So this information can useful for everyone planning to add amp.
The main problem was to run wires through firewall. There was no grommet in accessible place so I started looking for suitable grommet from inside. In drivers foot well (LHD) I noticed nice large grommet where was one thick punch of wires coming through. I couldn't see it under bonnet because intake piping was in the way.

So I made one sketch to make it easier for others:
1 - remove 3 clips holding intake pipe (bown)
2 - de-attach intake pipe joints from filter box (yellow)
3 - unbolt 2 bolts shown in light blue. One is holding filter box to the body and other is holding this valve to filter box
4 - undo 2 pipes which coming from valve from the ECU bracket
5 - undo battery terminals and remove battery (green)
6 - un-clip 3 plugs from ECU (purple)
7 - un-clip air sensor from filter box (light brown)
8 - undo 3 bolts under battery holding battery/ECU bracket (not shown in image)
9 - pull ECU bracket towards front end so you can better access to filter box. You have to unclip 2 dowels holding thick wire to ECU bracket(down below)
10 - undo breather pipe and 1 wire from filter box by un-cliping 2 dowels.
11 - remove filter box and you can see nice large grommet holding wires that go through firewall
12 - open cold beer



Now you have to get power wire through grommet. I took one thick hard wire, made one end sharp, attached power wire to the other end and punched it carefully through grommet from engine side. Then I dragged it all the way through from cabin side. I also made small cut into the grommet from cabin side so I could pull thick wire trough.
Then I re-assembled everything under the bonnet. It's a straight forward job. Just make sure you connect 3 plugs to ECU and plug to air sensor back before you reattach battery.
After that I installed fusebox to power cable, bolted fusebox to ECU bracket, removed fuse and then connected to battery + terminal (finished picture later today).

So next step was to route wire to boot.
Again, easy job.
- unclip plastic sills front and rear
- undo front kickpanel plastic nut, remove kickpanel
- route wire under kickpanel, pull carpet back from sills area. You'll see some white plastic clips holding wires. Put your power wire to the same clip and run it to c-pillar.
- Now either you remove C-pillar lower covers or use the same thick wire method to run it through. If you pull lower cover slightly, you can clearly see the opening to use. I did the second option.
- if this is done, continue until rear seat bed. Pull seat bed to the front (as you want to fold seat-back) pull the carpet piece and run wires all the way to the trunk.
- reassemble kickpanel and sills.
- open second beer

Next step is to select position for amp, run RCA wires, speaker wires, place Hi-Low converter etc:
to be continued...

Excellent Post, & may be answering a query I recently put to the Forum asking if anyone had done this to a 2010 T31 - which must be pretty similar to yours...

I may be pre-empting your next instalment but I would be interested to hear why you seem to have chosen to site the amp in the boot (I would prefer under a seat which is where Bose models placed the graphic equaliser) & also why you are deferring the speaker change - wouldn't that upgrade make a significant difference on its own, & anyway you'll be increasing the power to the existing ones / can they cope ?

Also, if you're keeping the HU (as I want to) I'd be interested to read in your next Post about the output from it & whether its a stock connection or you need to modify it.

Keep up the good work ! (I'll try to send a virtual beer for when you next take a break)

I'll write a post later today but regarding your question...
This amp is HUGE. It would not fit under seat. Of course, you can use smaller 4-chan amp and mono amp for sub and mount them under front seats but only digital amps are small and powerful enough. Unfortunately I´m on tight budget. Of course you have to remove seats and center console to mount amps under seats (not problem though, if you have spare time and large garage). And there will be always a question how and where you are able to secure your amps. Are you gonna weld some brackets to the floor or seat rails?
Second question regarding speakers - I'm changing speakers somewhere in the future. I believe they can handle some extra punch at least for some time. I upgraded my Lexus with similar approach and OEM speakers could handle everything (at least those couple of months I used them). They were Fuji speakers rated 17 watts RMS. Later I changed them to DLS R6A-s and difference was huge of course.

So here is how my fusebox and wire is looking

So here is how i plan to connect my OEM satnav stereo to external amp:
First always inspect your amp if there is hi-input (high-end ones normally dont have). If there is high-input then its just he matter of routing wires from HU speaker wires to amp hi-in. In this case amp will convert the signal by itself.
But in case your amp has low-input only (RCA), you have to use external pre-amp converter (referred as high-low converter).
So I choosed Connection SLI4 from Audison. It is active (powered) converter and it also produces remote signal for the amp.

So I just have to take power from HU, connect ground, connect speaker wires frum HU and route RCAs and remote to amp.
Of course you can find passive converters cheaper but you still need remote for amp.

I also bought 2 Y-RCA cables to get 6 channels out of 4 channel HU (no subwoofer output in HU)

So right before amp, I connect those Y-cables to rear channel RCA cable to produce copy of rear channels (so 2 pairs of rear channels). Then I connect one pair to sub-input of the amp and another to rear input.
Amp has switches to convert sub-channel to mono and to cut frequency's. So there I get my sub-input.

About Apm placement:
I decided to place amp into trunk. As it is some huge-ass amp, the best position was in pocket under trunk floor. The one where is no drawer. I do not use it anyway (stuff is sliding around and making noise) and about 1/3 of it is still usable.
So first thing I did was to drill two 25mm holes into this box wall. One is for power cable(marked red) and other is for RCA-s and speaker cables (marked blue).
Then I selected position for securing the amp (marked purple) and bolted it through this box. Important is that you can route wires around that and attach them to the each end.
Then there is one plastic wall covering rear seat fixing points. As my wires run through that also, I marked position of holes in box to that plastic "wall" and drilled holes to that also (marked red and blue).
Now I can route RCA-s and power cable through separate holes without them to meet each other (because audio noise). Power cable is running from left side, RCA-s and speaker wires from right side.



Now all cables, drilled holes and amp is not visible, when trunk floor is in place. So there can be no damage also (and its nice and clean to eyes).

Hea töö/ Good work!

Thanks for the location & amp connection info, it makes complete sense & will be very helpful to me.

Once again, fantastic detailed post.

I was wrong and youbwere right. They sound really cr**py now when amp is installed.
I need new speakers ASAP