radio in 1991 bmw 3series

Need help with this radio. I'm installing an after market radio in this vehicle and can't get sound to work. I have the constant switch and ground but the ground isn't all that great so i have to run another one. The problem comes with the speaker wires. There is one black plug that has 8 wires in it. Attached to that plug is a plug that loops two of the wires and another two go to some other plug. So I've tried disconnecting that second plug and just random testing to see if I get sound and I don't. I'm pretty sure I should just have the customer get 4 new speakers and complete re-wire. Any help is appreciated.

Does it have the fader roll knob on the dash?

No fader switch in the dash.