I just did my head unit/rear speaker/ amp/sub install a couple hours ago. I'm thinking I'm gonna have to upgrade my amp wiring, I used 8 gauge because it came with a kit when I bought some other accessories, but I can't turn it up more than half way without the amp going into protect mode. I took a die grinder and got the paint completely off one of the bolts in the trunk that holds the cargo net ring in place right behind the driver's rear seat. Still didn't seem to help.
The head unit part was fairly easy. Pop the little corners out underneath the cubby holes and you'll see some slots to put a screw driver or whatever you want inside there. That'll pop the bottom half loose, then you just have to wiggle till the ducts on the back of the air vents clear the space they're in and everything else falls out from there.
I went with a Pioneer FHX720-BT head unit. It's got a zillion colors to choose from, so I set mine up to match the gauges perfectly. It's got hands free blue tooth, aux, cd, amfm, pandora, yada yada yada. I cut my harness off and soldered all my wires correctly, and left the left/right audible chimes off so I didn't have to hear the turn signals anymore lol.
The wiring was pretty simple, just make sure you pull your accessory wire from something like the cigarette plug on the console. You don't have to pull the entire console off (like I did, doh!) you can just get a screw driver under the lip of the cig lighter and it'll come straight up.
For the amp I ran my remote and power wire down the driver's side, there's a gigantic grommet just to the left of the brake pedal that you can make a slice in, in order to run your wire to the battery. The interior trim pieces come off and on very easily, just make sure the slots are free and clear of wiring or you'll bend the tabs that go back into place.
The rear door speakers are pretty self explanitory, pop the panels off and you can get to the wire directly under the center pillar where the seat belt goes. I cut the clips off and ran my own wiring up through the doors with ease.
I am still unsure of a solid ground in the rear of the sedan, I thought I had a good one but it turns out I was wrong because I still can't get the amp to work to it's full potential without going into protect mode. I rebuilt a JL 10w6v2-D4 and put it in a vented box full of cotton and it sounds great. Even the factory front speakers with an aftermarket head unit makes a world of difference. My only concern is how long it's going to take for the rear view mirror to fall off lmao. Hope this helps.
opcos
