1992 W124 Sound System issue

[filp]

Hi,

My 1992 W124 originally came with Active Bass. I have aftermarket headunit wired directly to new front speakers. After replacing rears with 50W RMS, I ran [+] from HU to fader wire and [-] through cut 8 DIN wire. But rear speakers were quite quiet.
I wired the Active Bass using rear speakers as input. Checked door speakers with battery, seems to be fine.
But Active Bass never worked. It gets power 12V, fuse is good, gets 6V on the control wire (antenna/amp on from HU, measured from wire to chassis).

Today I found two sound system amps in the junkyard and rewired them. They don't work and now my rear speakers are quiet, since I wired them through the amps.

So most likely there is something in common in the failure of both systems.

Any helpful tips?

Also, I don't know what is the yellow wire on the diagram, so I connected it to input speaker negative (white) on both amps.

I took the sound system from 1990 car and realized that wire colors and numbers are appropriate for 1992 system, not 1990-91 in ETM.

Thank you

Update: I connected control wire to 12V and no change. Removed the amp, jumped speaker inputs and outputs on the connector and there was sound, so wiring is okay.