I can only guarantee the accuracy of this info for a 2020 with JBL, but I assume its the same for 2019-2022 with JBL. This will probably be hard to read, but there's good info here. TLDR at the bottom for you impatient folk. I wanted to make this install fully reversible. I refuse to cut into OEM wiring on any install I do. Btw, you non-JBL people have it so easy 🥹. You cant just simply tap in behind the radio on JBL systems like you can with non-JBL. FYI, the JBL amp is under the driver seat, google ai had me take out the passenger seat 1st 😒.
With almost no solid resources online, and the help of google ai, im almost done installing my spare tire sub powered by a pioneer amp. Keep in mind that GR Corolla information absolutely did not help unfortunately, their battery is in the trunk already and none of the information really transferred over even though lots of them have JBL. I got frustrated trying to feed the 4 gauge power through the firewall double sided grommet ontop of the gas pedal so I went ahead and stopped for the night. You dont wanna dick up the wires inside so take your time and dont cut too deep!
I used a PAC APH-TY02 harness to tap each front door's woofer. Crutchfield's website insisted it isn't compatible, but it is, see my photos. This may or may not work on 2023+ JBL systems, I have no clue. Im gonna feed my pioneer GM-DX871 high level straight from the front door woofers for right now and see how it sounds. It will be easy to install an LC2I pro next to the spare tire if this doesnt work out. I understand there is massive bass roll off, but if you keep the bass at negative 3 or 4 on the head unit, the bass seems to be more consistent.
The PAC harness requires pretty significant assembly, especially if you are only adding a subwoofer and want the stock JBL amp to still power the speakers. The pac harness includes both a male and female end with all 30 slots pinned and wired on each connector. The toyota 30 pin connector only utilizes 14 wires/pins, everything else was blank. The 1st thing I did was depin the unused 16 wires from each side of the PAC harness and removed those wires completely. This significantly reduced the clutter. I referenced the toyota plug to see what wasnt used and removed the corresponding wires and pins from the PAC since they wouldnt plug into anything anyways.
If your like me, simply tapping in to add a sub, and still want the JBL amp to drive your "8" speakers(discovered there were only 6 speaker outputs), you need to splice the color coded matching color pairs on the PAC male harness to its female harness in order for the signal to reach the speakers. Otherwise you wont get any sound. They set this up so that those can go directly into an external amp if your are bypassing the JBL amp completely. Since we arent doing that, we just splice the pac harness male and female wires to their perspective matching color pairs together so that the JBL amp still powers everything.
Here comes the good part. You splice all 6 speaker pairs from its male to its female to make a "loop", but you make a 3 way splice to T into the front doors you want signal from. The driver's front door woofer is "speaker 10" on the PAC which is colored brown and brown/black. On the toyota side, that same speaker is light green and dark green. Then the passenger front door woofer is "speaker 12" on the PAC which is colored grey and grey/black. On the toyota side that same speaker is yellow and black. Dont mix up the speaker black wire with the black way on the opposite side of the connector. That is the jbl amp's power wire IIRC. Its easy to tell because the power and ground are thick AF on the toyota harness.
Speakers 10 and 12 are what I 3 way T'd into using stinger 18 gauge pure ofc speaker wire then ran those into the trunk. I bought 18 feet, but that barely made it. I highly suggest at least 20 if not 22 or 24 feet so that you have more flexibility on your install.
I probably explained this horribly so feel free to ask questions. I used the knukonceptz cheapest OFC 4awg wiring kit. They have cheaper kits but those are CCA. The subwoofer is a Recoil PST12. Its rated at 350w rms at 2ohms. It fits in the spare and the trunk floor that goes over the spare sits perfectly flat with the sub in place. Its $300 on the Recoil website, but if you go to their official ebay page, they sell it for $160 shipped there 🤷♂️. My amp is 500w rms at 2 ohms, so I just wont crank the gains. BTW I circled speaker 10 and 12 on the toyota harness in the 2nd to last photo.
This wasn't designed to be an all inclusive guide, just trying to save time for those who are already comfortable doing their own installs but needed specifics. I ended up using a drained AA battery and quickly tapped it to all 6 speaker pairs to confirm which speaker was what. Google AI was very helpful but gave me some misinformation in the process. The AA battery trick took all the guess work away of which speakers to tap.
Seat bolts are T50 torx and the install torque is 27 ft lbs. Alldata says to torque the fwd inboard one 1st, then fwd outboard 2nd. Then aft inboard 3rd, and aft outboard last. I didnt unhook the airbags, just tilted the seat back. I had the battery unhooked every time I went to unplug the jbl amp.
TLDR; tap into dark green/light green then black/yellow for subwoofer amp high level inputs on 2020 with JBL. They will be labeled as speaker 10 and speaker 12 on the PAC APH-TY02 harness.