Add an AUX input to the Nexia Clarion head unit

It is decided - we open the radio. And we see that the manufacturer left a place under AUX. Inside the panel and on the panel board.
But on the board of the radio itself - no. Apparently, not that modification.
Using the scientific poke method, it was found out that you can connect in front of the preamplifier. By input CD or Radio. There is no point in connecting to the tip, there will be no control of the timbre, balance and volume from the regular controller.
Connecting to a CD also makes no sense. If the disc does not play, the preamplifier and the tip are in MUTE mode. Moreover, if you can still send an enable signal to the terminal, then the NJW1192 preamplifier chip turns off in software idle.
Some, however, circumvented this by recording silence on the disc. And include it in parallel with an external player. I know a lot, yes.
Another comrade connected the connector directly to the radio output . The result was an interesting effect: as soon as the player is turned on, the sound of the radio disappears, and the output signal comes from the player. I checked it myself.
True, if you pause the player, you hear a very quiet sound of the radio. I believe the matter is in the different output resistances of the terminal amplifier of the player and the preamplifier of the radio module. The first just drowns out the second. This option is also dismissed. If you do not mind the radio, then no one guarantees the safety of the player in this mode. And this is not gut. Players and phones (in music playback mode) are now expensive.
So - cut it. We cut the lines from the radio to the preamplifier (R-LO and R-RO) and solder the switch into the cut. Points 1 and 2 are very conveniently located there, so you don’t need to clean anything. The main thing is to cut the tracks between these points and the soldering of the radio module (3 and 4).
The second line to the switch, respectively, from the 3.5 connector. Capacitors for insurance. Capacitance from 1 to 100 uF. You can do without them, if not sorry to risk a player.
Check, collect:
Install back. Everything works. Radio mode - AUX is switched by a toggle switch.