Plug the matching shorter power cable into the longer one so they snap together (they can only go one way).
Now you'll want to trace the red power wire back through the connectors. We suggest using a multimeter to be sure. Put 4 AA's in the holder and turn it on. Then use a multimeter to measure the voltage between the cable wires. One way will be about -5V and the other will be +5V. When it's reading +5V the red handle is touching the positive wire. In this example, its the one on the right:
Cut the positive wire short by about 1"
Turn the board over, and solder the ground wire.