Amazon product B09DTY8PMD It plugs in between the stereo and the feed TO the speakers. You cut into the FR and FL wires ON THE EXTENSION YOU JUST INSTALLED (not the factory wires) and tap that signal to go to your subwoofer/amp. That's 4 wires you're digging into, +/- for front left feed, and +/- for front right feed. And that's it. Wrap the extension in some tesa tape or some other cloth tape to reduce any noise from the extension wires rattling from inside the area back there, and just to keep things neat.
Thank you for your reply!!!!!! Really appreciate!!! And could please share your upgrade solution? Like speakers or subwoofer.
if you are looking into a different location and possibly a better quality harness in a potentially better location, here is one someone on the forum used. (Thank you PhoS!) This plugs into the JBL amp under the seat and could allow shorter wire runs based on application. 30-pin Subaru Harman Kardon and/or Toyota JBL Amp jumper - Splice Harness to add Subwoofer Since the only upgrade I plan on at the moment is a small-ish powered sub, likely in the trunk area then this harness represents less wires to run and a less evasive install.
