O.k., I finally did it, and here are instructions to get all speakers on line with the Kenwood D558BT in a Limited w/nav (of course, nav will be gone, but Bluetooth, Sirius, Pandora and Ipod control added). Some of the following may seem elementary, but I did not want to be talking over anyone’s head. Simply, as I researched this, everyone was talking over my head. If you are going to follow these instructions, read the next post as well.

Tools/supplies needed: Star head drivers, HU keys (Walmart or come with the unit); wire stripping/crimping tool; coat hanger (pulling wire for mic and left rear speaker under left dash); needlenose pliers (to form the hanger pulling tool); something like forty connectors (see images two posts down); ratchet set (rear speakers and amp cover); prying tool(s) (removal of rear speaker covers); connector wire ( 4 seven foot runs. I used 18 gauge); phillips and flat head screw drivers (because you should never go anywhere without them); antenna adapter, Sirius/XM radio adapter; and Metra 1784 harness.


These instructions are WITHOUT WARRANTY, EXPRESS OR IMPLIED, and provided gratuitously. I am a neophyte at this stuff, and you should not necessarily trust me. Do your own research, reach your own conclusions, and make your own installation.

Here is a description of what you are dealing with:
1. Car radio harness (this is the harness from the vehicle which the purchased harness will plug into);
2. Metra 70-1784 harness;
3. Head unit (HU) and the wire set from the back of the HU;
4. Each rear speaker removed including cutting the four wire harness attaching to the rear speaker. The cut should include leaving sufficient pigtails on each side for splicing in new wire or jumping in the old set-up to reattach the factory HU at a later date.
5. You will be ignoring the RCA’s on the back of the HU entirely.

First, the correct harness is the Metra 70-1784. It may be that a 1786 will work as well, but the RCA’s are not used.

1. Pull the old head unit (“HU”) using the keys that came with the Kenwood.
2. Install the HU sleeve for the new HU. Just snaps in, and I did not find that there was a need to bend tabs.
3. In the 1784, install the blue/white wire in the spot matched to the new HU wires and car harness.
4. Switch (cross) the red and yellow wires on the 1784 as you splice them in to the HU wires and the 1784 wires.
5. Splice in the remaining matching wires on the 1784 to the wires coming out of the HU (color match);
6. Identify the green and violet pairs coming out of the rear of the HU (solid color is +, and the wire with the black strip is -. The green wires are rear left and the violet wires are rear right as read by the HU. These should not yet have been used;
7. Remove the rear speakers:
a. Pull the metal finisher at the top of the rear of the door closure (black w/3 screws);
b. Move the seat to its most forward sliding and tilted position;
c. Remove the pin from the carpet on the vertical rise of the carpet up near the bulkhead;
d. Remove the round finisher at the plastic bulkhead cover (this is necessary to avoid tearing the carpet (too late for me). Can be done by hand, just apply pressure and turn counterclockwise;
e. Pull back the rubber finishing strip from where the metal finisher was removed to the sill plates;
f. Remove the rear speaker grille (pressure snaps in piece of some delicacy. Push and pry top snaps (unseen and behind) from multiple spots until they pop. This will release the pressure on the same snaps at the bottom, and it will fall out.
g. Fold carpet back exposing rear speakers (note, top of carpet has a flap tucked into the plastic finisher at the top of the bulkhead);
h. Remove the three nuts evidently holding in speaker. Remove the black plastic domed cover. This piece is not part of the speaker assembly, but a clamp for the speaker assembly.
i. Cut the wiring harness to the rear speaker (four wires). Do this before the final speaker connection (i.e., before the clip harness at the speaker) and not before the final speaker wire connections. The cut should leave sufficient pigtails on each side of the cut for splicing in new wire at the speaker, or jumping in the old set-up to reattach the factory HU at a later date.
j. Entirely remove the speaker from its cove. The second black cover (metal and not domed) attached to the bulkhead will come out with the speaker and the holes match the previously removed cover (plastic);
8. Determine the wiring to the speaker with the four pigtails hanging loose (two of these were a twisted pair). To do this, look to the attached schematic. The relevant picture is the small one at the lower right. At least in my car (an end-build 2008) there was not a single wire that matched the color coding on the schematic—NOT ONE. Therefore, I have no idea what other cars may relate or not relate. The image on the attached schematic appears to be a front image of the female connector to the speaker wires with the clip at the top. It is actually attached to the speaker assembly, but you cannot see it as the connector with the four sliced wires is already plugged in. Nonetheless, you can trace directly which wire is the corresponding pigtail to the numbered spot on the pigtails. The goal here is to match the HU green wire (left) or the HU violet wire (right) with the #1 spot on the image. These are to be connected to the corresponding wire that is loose from the speaker harness. The wires which correspond to the #2 and #3 spots on the diagram are to be connected to each other at their pigtail ends. Finally, the HU gr/bk wire should be connected to the left #4 spot. For the right side the HU vi/bk wire should be spliced to the wire corresponding to the right #4 spot. CAUTION: While attaching the HU and the rear speakers, you should have already figured out your wiring routing and been largely in place. The HU connections are at the back of the HU, and must be extended to a place where you can hide them from inside the HU cavity to the speaker location. Mine, to a point, parroted my post on the mc wiring.
9. Returning to the HU, the antenna is the wide clip from the wiring harness, not the plug in from the original HU (the other is the satellite data connection for the nav.). Plug in the antenna adaptor to the HU and clip on the antenna connection.
10. The Sirius/XM radio adaptor (buy one, write down the code, and save it) attaches to the multiplug on the back of the HU. Plug the Sirius/XM antenna into the Sirius/XM adaptor. Contact Sirius/XM on the net or by phone to start or transfer service.
11. Test radio and all its functions, pair your phone.
12. Reattach rear speakers to body.
13. Finish hiding the wiring down the left and right sides of the doors/car/bulkhead.
14. Reattach carpet.
15. As you are sliding the HU into place, try to keep some order in placing the car harness and clip, Sirius/XM adaptor, antenna and wiring connections in the cavity behind. You will quickly run out of access as you put in the HU, and the final elements are truly just shoved into the hole preceding the back of the HU. Push until clicked into place.

That should be the end of the connections, and voila, you’re done.
Some insights as to what just happened and what I have been able to discover. While there is no reasonable explanation why the rear speakers don’t run on a simple two channel plug and play, on the Limiteds, they most certainly do not. The best, but inexplicable, explanation I have yet heard is that the rear speakers also have a data trigger that moves through the original HU, and that is now gone.

What has been accomplished here is that the rear speakers are running off of the amp in the new HU, and bypassing the factory amp entirely. What occurred at the speaker is that the parallel wiring of the dual coil rear speakers which formerly ran from the amp has been converted to serial wiring allowing for the two wire set-up from the HU. What you are seeing is + into coil #1, neg. from coil #1 running to + at coil #2, and finally, the neg. from coil #2 returning to the neg. at the HU.

There may be a way to do some or all of this from the factory amp—I don’t know. Nonetheless, with the wiring colors in my car being entirely unmatchable to the factory service manual (both at the amp and at the rear speakers) this option appeared impossible to me. Also there was a connection and splt-off from the amp to the rear speakers in some unknown place, and wires to the rear speakers at the rear speakers did not match any of the wiring colors at the amp.

Finally, a simple reference to the attached diagram shows that your senses, and not the factory’s drawings, must be where the information comes from. Pointedly, the factory did not even know what they had as they labeled simple speaker wire a power wire when it clearly is a speaker wire for the second coil.

 

First, having run this for a day now (beyond just a test), this does sound better than the original, has far more control (including fade), and all parts of the HU seem to work as indicated. There is a touch of loss to hard thumping from the original (probably due to running off of the HU amp rather than the vehicle amp and powering two speakers in series rather than two in parallel), but there remains some thump and better control, and unless you are an avid 'cruiser,' the base is more than sufficient. A couple of additional thoughts and some clean-up are in order. The black plastic cover is not merely a clamp as stated, it is also the receptacle into which the speaker grate plugs snaps. The hard part of the carpet is the screw at the plastic bulkhead cover, as, through abundance of caution, the engineers have a hole in the carpet overlapping the screw at the top of the bulkhead. If you can get it done without removing the carpet from this screw (i.e., only marginally folding back the carpet), more power to you. If you must remove it, I cannot figure out a way short of dismantling the entire bulkhead finishing, and that seemed too much. Both sides of my carpet tore at the hole, but it is entirely invisible and also continues to be firmly held in place by the flap under the plastic bulkhead cover. Also, before final plug-in and speaker re-attachment, while I trust this would be done, every open wire at the HU and the rear speaker sub-harness should be capped off in order that it cannot short to anything. If you take down the front passenger floor and expose the amplifier, wiring to the right should be easy and evident, coming out the back of the radio cavity, into the netherworld behind the floor/amp cover, and running up the door sills.

 

I used the screw type. Find them more certain and less likely to result in an open.