I dint know there were sub wires under there. If they are outputs, it seems as though they should be able to power a sub. If a power "on" lead is under there too with a power wire. Looks like you may need to do some checking with a voltmeter at the least to find the power wire, then the power on and outputs should be easier to ID. Ill look around on the net for a wiring diagram.
OK look here, it may help:http://www.wiringdiagrams.us/smart-car-fortwo-wiring-diagram/