Where does the black and red wires go on a L reg Transit altenator?

Van had flat battery, charged it & started ok. Put multimeter on battery only got 12 V with engine running, fitted a spare altenator (found out previous owner had taped female blade fitments to round ones) removed blades and refitted to repacement unit (screw terminals) but still onlt getting 12V from battery when engine running and battery light won`t go out, I have fitted the red wire to the left hand side terminal and the black wire to the middle terminal (this was the way it was previously fitted) there is nothing on the right hand side terminal, is this right?
Your thoughts would be appreciated.