Aux not working - all troubleshooting exhausted

Hey everyone!

So, the aux/CD button no longer switches to the aux input when pressed. So far, I have:

1. verified the 3.5mm audio cable is non-defective and fully seated in the connector with loud music playing
2. soldered the points together as shown in this post Aux Jack repair | PriusChat
3. removed the aux module from my car and installed it in another vehicle. It works perfectly in that vehicle.
4. Installed the working aux module from that other car in my car. In my car, as expected, the other car's module did not work.
5. Checked for any shorts in any wires along the chain from the aux module to where it feeds into the head unit
6. Unplugged the aux battery and waited 10 minutes before reconnecting
7. Checked for Audio codes in service mode (no codes found, pressed and held "clear codes" for 3 seconds regardless)

This all began after I spliced into two gray wires in the connector at the back of the center console (these original wires were not cut through at any point - I divided the strands of the original wire in half, fed the strands of the new wire though the middle, and then intertwined them all, so as to not sever the original wire). I used this added wire as a 12V trigger to power on an added subwoofer - it worked perfectly for this. However, despite the original connection pathway being maintained, something is preventing the car from switching to aux mode. I then removed the cable that was spliced in, returning the gray cables to their original, uninterrupted state, re-coated them with electrical tape, and repeated the troubleshooting steps above. Still no dice. Does anyone have any other ideas of what to try here? Pulling my hair out a little bit.

Thanks so much for your time!

 

Thank you both for the input! @dolj It does seem that discontinuity is the likely culprit, but no section I've interacted with at any point has an interruption I can find. I'll use a voltmeter later today to verify continuity from the input to the head unit, though, so that hopefully that can be ruled out or pursued further.

@ChapmanF The head unit doesn't allow selection of the aux input at all, unfortunately, either through the CD/AUX button or the Mode button on the steering wheel.If there's an issue with the detection circuit within the head unit, do you have an idea of how that might be corrected?

 

Update: I have used a multi-meter to verify continuity of all wires of the aux module connector (green/red/gray/white), from the connector that attaches directly to the aux module to the connector that enters the back of the head unit. The pathway is not disrupted, so it must be that a detection circuit within the head unit is malfunctioning. Anyone have an idea of where to go from here? I'd really hate to replace the head unit over this. @ChapmanF

 

I suppose I'm just a little confused - my understanding was that the detection circuit was within the aux module itself, which is what the aux jack repair linked in #2 of the first post is supposed to correct. Is there another detection circuit? About to hunt through a wiring diagram to see if I can find any answers

 

You make some good points and I really do appreciate the input. The only thing is that I'm fairly certain an issue within the aux module itself has been ruled out already, given that:

1. another aux module, known to be working, does not work in my car
2. my aux module works perfectly (including auto detection/turn on) in the other vehicle