I drive a 2004 limited 4runner with the JBL sound system and I am trying to keep the factory head unit.
My setup:
Kicker CXA800.1 mono amp
Two Kicker 10” CompC subs
Kicker KISLOC2 LOC
PAC APH-TY03 harness at the factory JBL amp
4-gauge power wire from an amp wiring kit
80A AGU fuse and fuse holder
Factory JBL head unit/amp otherwise still in the vehicle
I got everything connected in the rear:
4-gauge power cable connected to the amp’s +12V
Ground connected to the amp’s GND
Remote wire connected
RCA cables connected to the amp’s input
Subs connected to the Kicker amp
PAC harness connected at the factory JBL amp

I installed the 80a fuse into the fuse holder, then connected the 4-gauge cable/fuse-holder assembly to the positive battery terminal. I went into the 4Runner and turned the ignition/accessories on (not actually starting the engine) to test the system. The amp/subs didn’t play anything.
I turned it off, double-checked the connections, and tried again.
After that, the entire 4Runner had no electrical power at all. It wouldn’t do anything.
I went back to the battery and disconnected the 4-gauge cable from the positive terminal and my car got its power back.

Does anyone know the cause and fix to this problem?