OK, here's the temporary solution:
Just used two wires from this black plug and found two in original changer plug. The case is that at the moment I've got mono sound but it's playing both channels on all speakers. It's paired with my mobile and handsfree is working as well. I had no time left to find stereo connection and just had to put all things back into place. I will continue the work probably next weekend.
The other problem I had is that I can hear some interfering buzzing sound when listening anything from the device.
ps. the black connector doesn't fit cd changer plug as those are both male. I also cannot use the female plug as it's slightly different