Radio Harness Wiring-Hard Mode

[Drakethefirst]

I have done many head units, speakers, subs, and amp combo and projects. However the 4runner JBL premium system made me learn a new way of wiring. I am new to this so please any experts chime in and correct me if I am wrong and give some advise.
So I have been researching this system for far too long, I have put off upgrading the head unit because of the cost of all the damn harnesses you need to keep your steering wheel controls and your amp and sub. Then I started looking into why? The systems that I have worked on before were the standard head unit-gives power to the speakers. If you want an amp and sub then you add them and wire them to the head unit-done.
However this system is different where the amp is now the main attraction. The head unit gives a signal to the amp which then gives power to the speakers and sub.
So with that knowledge and searching on crutchfield for the best system I found the harnesses. One of those is the Metra 70-8117 amp bypass, which I initially thought plugged into the factory amp harness and then into your new amp...nope. It is a harness that plugs into your factory amp harness to then run those lines all the way up to the head unit so it can be used as a standard system I just listed above. But that wasn't the worst part...by using this method you are now bypassing both your rear pillar speakers and your center dash speaker because those are wired or powered separately from the door speakers. This made me question, why is this the only option? Why can I not just make my own harness from the factory amp harness that already has the outputs for the door speakers and tweeters?
I want to know if anyone has gone through and did this the hard way instead of using all these harnesses? Has anyone spliced into the factory amp harness and kept all their speakers while using an aftermarket amp, woofer, and head unit?

My ultimate goal is to replace all the factory speakers with 4ohm speakers from the 2ohm, replace the factory head unit with an aftermarket touch screen with backup cam and carplay, upgrade the woofer to something better and keep the 2ohm, and replace the amp with a 5 channel that can handle all the above. But is it possible/am I missing something?

 

[hankd]

i don't have much to offer here, but my 4th gen came with the jbl system and somebody had installed an aftermarket deck and it was a real mess. so i took out the deck and poked around a bit and tried to put it back together.

i used a harness from axxess for the steering wheel controls and it picked up my cheap pioneer deck right away.

i didn't want to deal with the amp so i bypassed everything completely and ran new speaker wires to the doors. you can get into all four doors without too much hassle. i just used used 3 way 6x9s in the front doors and didn't bother with the tweeters. all four door speakers had special built in mounts but i got some cheap adapter brackets on temu and the aftermarket speakers fit no problem.

i didn't do the centre speaker or any stuff in the rear. so yeah super basic setup.

i have a 5th gen with a jbl too. on the 5th gen there is an area near the passenger kick panel where you can tap into all of the speakers but one.

 

[simple]

i don't have much to offer here, but my 4th gen came with the jbl system and somebody had installed an aftermarket deck and it was a real mess. so i took out the deck and poked around a bit and tried to put it back together.

i used a harness from axxess for the steering wheel controls and it picked up my cheap pioneer deck right away.

i didn't want to deal with the amp so i bypassed everything completely and ran new speaker wires to the doors. you can get into all four doors without too much hassle. i just used used 3 way 6x9s in the front doors and didn't bother with the tweeters. all four door speakers had special built in mounts but i got some cheap adapter brackets on temu and the aftermarket speakers fit no problem.

i didn't do the centre speaker or any stuff in the rear. so yeah super basic setup.

i have a 5th gen with a jbl too. on the 5th gen there is an area near the passenger kick panel where you can tap into all of the speakers but one.

My amp just died I think. Instead of replacing it I'm thinking about just running new speaker wire as well, and hooking it up and building an 'OEM connection' harness from a Metra kit. But I'm curious how I do it with the non speaker wires. How did you get the other wires connected... the power, antenna, lighting and the other wires that aren't speakers?

 

[hankd]

that part is actually pretty straightforward. you can use one of the metra kits to plug into the oem harness and it will break all the wires out individually so you can tap whatever you need and leave the rest. the kit instructions will tell you which one is power, ground and acc.

i didn't have that same kit. but when i took everything apart, i saw that the previous owner had spliced into the power wires before they got to the oem harness. if you search the forum you can find what colors the wires are.

the antenna is a standard plug that all stereos seem to share.

i can't remember if i had a wire in my stereo for the lighting. you'll probably run into that information as you're researching other threads.

the trickiest part about replacing the jbl systems is the speakers and the speaker wiring. i don't think the jbl speakers work great with aftermarket decks either due to the impedance mismatch, not 100% on that tho

 

[ArthurKotb]

Have you spoken with one of the techs at Crutchfield? I have used them in the past for another car I have and they were very helpful with swapping out the head unit and amp, keeping the steering wheel controls. I have the premium JBL system in my '04 but have never modified it, other than to add a Bluetooth device so I could connect my smartphone to it. (really works well)

Try a chat or phone call with them.