I see. So the extra cable was not a single wire, it was a multi-conductor cable. If you'd said that from the beginning, I would have been able to determine that it wasn't the antenna power. The power antenna leads are almost always a single wire.

So it seems that second cable is some sort of a serial communication system between the antenna box and the radio. Makes sense in a diversity setup.

Glad you found the correct wire before trying anything. Plugging 12v into that line might indeed have damaged that antenna control computer.