So quite a few people have installed a powered subwoofer so I'm not claiming to be the first, it's just there's no wiki article.
I've previously had a MY2006 (non-airbag dash) and that had a subwoofer fitted under the dash in the pax footwell. It seems the facelift dash (I have a MY2010 Exige) won't easily support something suspended from beneath the pax airbag so the logical decision was to place it behind the foot rest.
I had some help from pinkie and litton4 regarding their installs which helped me on my way but I don't think either of them put their subwoofers themselves so they provided a bit of observation and heresay from their installs.
I have experience of a previous installation in a Cayman of a Kenwood KSC-SW01, but choose a KSC-SW11 for this installation for 3 reasons. 1. the KSC-SW01 has a more limited remote control. This is not a problem if you have a multi-functional head unit that supports all the config for a subwoofer in the software (for the Cayman I had a Double DIN touch screen Kenwood DNX model) 2. the size difference is actually fractional. 3. The KSC-SW11 is a symmetrical design and so anticipating its location I thought it may look aesthetically more OEM.
The wiring for both Kenwoods is identical, and I planned to used phono leads to connect to the head unit.
I have a fairly basic Alpine CDE-9872RM
So consulting the wiring diagram there are basically 5 connections to consider.
Litton4 had suggested to me that he believed the power for his subwoofer had come from the jump start posts under the inspection hatch. After a quick reccie I found the fuse box and obviously plenty of cables leaving that area and heading into the cabin. Having a look under the pax footwell I spotted a bundle of cables heading out through a grommet just underneath where I imagined the fuse box to be... so I made a small incision into the grommet and a poke of a graphite rod (technical version of a coat hanger) and I found it appearing underneath the fuse box. This confirmed I had a run for +ve and earth. So starting from the outside in (yellow power cable for the sub has a separate 10amp fuse near the O ring connector) I classicly duck taped the other end of the yellow cable (bullet connector) to my rod and retrieved it into the cabin. I found it easier to remove the fuse box to get access but be careful not to lose the nylon washers underneath.
So the +ve cable separates from the block/plug thing with m/f bullet conectors. The earth however is two cables spliced into one and is connected to the main subwoofer block that accommodates the other connectors and won't practically squeeze through a grommet. A trick I used is to piggyback on the +ve cable as it is so long you can easily attach the earth to it (more duck tape) and then retrieve it by pulling the yellow power cable from the outside and still leave a comfortable tale in the cabin. Bingo. 2 cables done well once wired up.
|+ve and earth connected to jump start posts|
I had to swing the +ve cable around so I could put the red insulation cover back on.. (I also dropped the original nut somewhere onto the floor pan. Doh!)
So the next connundrum is how to connect the Phono and blue/white power control (subwoofer trigger) cable to the head unit.
|2m phono cables|
This was much trial and error and after a failed attempt trying to poke them up through another grommet I discovered there's a track that runs along the top of the oddments tray and below the airbag part of the dash (long red horizontal arrow)
|cable run behind airbag fasica|
I removed the side panel in the direction of the blue arrows (unclip it from the front edge gently) and clearly you will need to extract the head unit at some point. Now is a good time as I found there is a recess underneath the cage on either side that will enable you to get the phono and power control cables discreetly to the back of the unit unmolested by the HU.
Power Control Cable
The Power control cable (blue/white) will need to go left to right along the same track as the phono cables (the plug on the other end forces this issue).
With the side panel out you could also route the remote unit cable along the oddments shelf and I used the groove in the rear as a cable track for the telephone style cable. All these leads can then be routed down behind the side trim and for it to emerge just underneath. You could put the side panel back now or wait until tidy up phase at the end.
|Cables hidden behind side panel|
|Cables emerge under shelf|
So now you have; - the telephone style cable for the remote with the telephone plug to plug in directly to the subwoofer - two phono connectors to mate into the ones from the block connector. - the +ve cable from you earlier efforts with a bullet connector (to connect with the bullet socket back to the main block) - the earth will already be connected into the main block - the power control cable (blue/white) that senses when to turn the subwoofer on and off (straight into the main block)
Head Unit connections
There should be only 3 connections to do. The 2 x phono ones are simple right and left. The CDE-9872RM does not have a power control terminal and so I crimped it onto the red power connector from the head unit using a quick splice electrical connector (I had the wiring diagram from the manual to confirm). This senses when the subwoofer should be in the "on" state and makes sure its "off" when the ignition is off.
|Quick Splice electrical connector|
So now to test. Presuming it's all working you can now work on how to fix it to the wall. There's a nasty big bolt on the Exige just where you don't need it and the wall isn't exactly flat so I used a load of super strong double sided tape. It may not be quite up to track abuse (UPDATE: It WAS up to track abuse) but if I find that's the case in the future I'll investigate some alternatives which may involve a drill as it comes with several brackets and options including one to ensure the cables make a flat exit. Some of the cables are long by design (to allow for other installations) so you'll have a lot of cable ties to do to tidy up the excess.
|In situe, time to tweak the settings and tidy the cables. You can see the remote at the back of the shelf (will glow blue when power is on)|
The two loose cables you see in the last image are a USB power supply (run on a 3M USB cable from the 12v socket on the back wall between the seats) and the iPod cable (from the Head Unit) installed at the factory.