If there is only one set of terminals then its only a single voice coil sub, unless its broken off or something, lol. Just use a multimeter to double check its ohm rating. If its a 4 ohm sub it wont be exactly 4 ohms, the meter measures dc resistance and it might be like 3.5 or something. Just wire them in parallel to load it down as close to 1 ohm as possible. Connect all the positive and negative terminals together. I sometimes even like to measure the speaker wires right before I connect them to the amp, so I know for sure what ohm rating the amp "sees."

PS If the amp only sees 2ohms instead of 1, then it will only output half its power. But at least it wont overheat, haha.