Rubberduckie-
Don't take this the wrong way...its apparent you have never done ANY type of automotive work, let alone work on an electrical system. I wouldn't advise trying to fix the problem yourself. Dealing with the electrical system in these cars can/will cost a LOT more if you screw up...and it doesn't take much! The computers on cars these days can blow very easily and this will cost thousands to replace. Rather than taking advice from the great people on this board and trying to apply it alone, I think you should either return to the mechanic who supposedly "fixed" it or if not comfortable doing that, go directly to Porsche. The high costs now will seem small in comparison to what can happen.
In the future you can start doing the small things to this car (such as oil changes, brake pad changes, etc.) by following this boards recommendations and learning about your car slowly. Before you know it you'll be a shade tree mechanic with ample ability to fix common problems you will encounter with this car!
