I bought a pfranc plug (www.pfranc.com) and then using a small plastic enclosure from A1 radio, I added a serial plug to the box. I then stripped an old car cellphone cigarette lighter and changed a few resistors to step down the 5V output to the 3V I needed for my Etrex Vista. I then stripped an old mouse of its tail and connected the PS2 plug to the cigarette lighter. The data line from the serial plug goes straight through to the pfranc plug whilt the power comes from the PS2 port via the cellphone cigarrette lighter.