[mac30605]

I have searched the forum but haven't found what I need. I am reolacing the stock radio in my '86 928 and can't firure out the wiring. I got an adapter to adapt the 8 speaker wires to 4. I connected those wires to the adapter, connected the ground wire, the battery pos. And the red lead to the ignition. But there is a small white wire that branches to two, one to the wires coming from the speaker harness and also alongside the antenna wire. What does this wire connect to? With all the wires connected, I get sound but only when the volume turned to max and very weak. It's an Alpind radio, any suggestions?