I'm definitely not an electrical engineer, but I could swear to you the Magsafe doesn't have a third wire for grounding. When I cracked apart my Magsafe plug to try and re-solder it (after the wires were bent out of their heat shrinks and melted the plastic a bit) I found three solder points on the Magsafe mini-circuit. The ground was right below the 16v+ on the left and negative was on the opposing side of them both to the right. The only point I found the ground wire connecting to was the negative, which doesn't make any sense to me.

I cut down the wire some more and only found two. What in the world am I missing here? Does the negative and ground run on opposite sides of the wire or something?


EDIT: http://pinouts.ru/Power/magsafe_power_pinout.shtml
Here is a link to the Magsafe pin layout.