So I'm definitely a novice this sort of thing as well and have never installed a car stereo or speakers before. It really becomes easier to tackle if you start in stages.
First thing to decide is whether or not you want to bypass the factory system. I read a ton of info and thought I would be able to reuse the factory stuff but I never found someone who had great experience with the adapters and the factory amp. This necessity caused me to go for an entire overhaul.
First step is figuring out the rear amp and subwoofer setup. I wanted to keep the stock enclosure and just run an 8" sub. I found the Kenwood KFC- XW800 excelon was a great choice, tons of good reviews, and fit in the stock location without even having to dremel away interior material for depth. it literally drops right in.
Next was the amp. The best choice I feel is the excelon XR900-5 b/c it literally fits in the stock amp location with minor trimming. It was just too expensive. I chose a different 5 channel amp that I'm mounting on the rear passenger seat back.
As for whats involved.
Sound deadening is paramount IMO b/c it really helps with sound. Tons of products to use I just chose Dynamat Extreme b/c I was most comfortable with it. I chose to remove the rear seat backs, rear side panels, carpet to get to the bare metal on both sides and up to the second row seats. This is not that difficult or scary. Just take your time, read the threads on this forum and it'll be pretty easy. Be careful with the doors. Dont block the drain holes at the bottom and start from the bottom and work your way up. Overlap with a shingle effect for proper water runoff
Second is running the wiring for the sub, amp, and speakers. This is the most involved aspect of the project IMO. Start with the Sub. You can reuse the existing grommet for the factory wires and run your new wiring through that. Quick note, push the grommet into the subwoofer enclosure instead of trying to pull out. Its much larger on the inside than the outside. The speaker wiring I haven't done yet but its basically removing the door panels and running the new wire. While the door panels are removed you can install your new speakers, sound dampen the door skins while your at it. The benefit of running all new wire is that you do not need to touch the existing. Just remove the speaker, leave all the wiring in place and run the new wire through the door loom to your new speaker. Take your time and use a wire coat hanger. start at your speaker which will furthest from your amp and work back to the speaker that is closest.
Decide on where you want to place your amp and run all the speaker wiring to there. Run your amp power wire down the passenger side wiring chase located under the door sills. You can also run it down the drivers side door but punching through the rubber grommet is more difficult on the drivers side than the passenger side. The rubber grommet is really a work of art. Snip the small nipple portion of it off. Then insert a screwdriver and pry back at an angle. It will take some time but you'll get the inside part out (hard to explain but I'll upload pictures later). The outside grommet opening necks down inside the grommet so you need to snip the entire inside portion if you are going to use 4 gauge or larger wire. Think of it like a collapsible bowl (frontrunner flatpack kitchenware set) that you need to make inside out.
After the wiring for the speakers to the amp is in place your pretty much set. Get yourself a metra ASWC-1 to keep the factory steering wheel controls, pick out your headunit, and connect it to the vehicle. I am still researching the best plug and play solution for this. Taco Tunes makes plug and play harnesses for the tacoma so I'm waiting to hear from them if they offer one that will work with the 4runner.
Most important is to take your time and start 1 section at a time. It'll mean your car is down for a bit longer but you can feasible get the interior apart, sound dampening down, sub installed in 1 day. Then second day is amp placement, amp power and rear speakers and sub wired and installed. 3rd day would be front speakers and wiring to the amp, 5th day would be head unit and RCA cables to the Amp.
Parts You will need
1. 4 gauge amp install kit (I went with Knukoncepts for all my wiring). The knukoncepts one comes with 1 set of RCA with a remote turn on lead. I'm using this for the sub channel. It also comes with 20' of speaker wire.
2. 50 feet of speaker wire
3. Channel A & B RCA cables (again i used KnuKonceptz)
4. Metra ASWC-1 if you want stock volumn and channel change
5. Back up Camera (great time to install since everything is apart
6. Sound Dampening (Dynamat Bulk Pack worked great and was enough for my entire car. I did the rear hatch, rear floor, subwoofer enclosure, rear sides and all 4 doors)
7. Amp
8. Sub
9. Speakers
10. Head Unit
