TwoFifty

I'm trying to install an aftermarket radio to my non-nav 2012 IS.

My first try with the Beat-Sonic SLX-140L adapter failed. As I learned today this one is spefically designed for the north-american spec IS models.
So my backup plan for doing this without the Beat-Sonic is to retain the factory radio, leave all cables connected and tack it somewhere behind the radio under the dash or in the glove box --> this should keep the HVAC, hazard lights and airbag light functionality.
In the old position of the OEM radio/cd-player I'm going put the aftermarket head unit with a fascia kit.
The new head unit will be connected directly to the old OEM radio / cd-player.

The only thing I need is a depiction of the Pin assignment on the OEM connectors to the OEM radio / cd player.
Google search didn't deliver any result for the unit I have. But as example something like this would be great:
But only for this unit:

PIONEER, ID=P3830
86120-53B00
DEX-MG8497ZT
AUDIO-AM/FM DVD CHANGER 5.1CH 14SPEAKER

If someone can help me out here I'd be really glad to finish this conversion because the OEM head unit is driving me crazy...