Help! I need my car back! Weird electrical problem 03 Sable.

I'm writing this for my friend who's not on web.
He has an 03 Sable, he was laid off for a year
and occasionally he had a problem with car not starting
but I guess he didn't have to get to work so no big deal.

Now when he goes back to work, in the morning he gets
about halfway to work, maybe 10 minute drive, and when
the lights are on the entire electrical system shuts down,
lights go off, etc. If he can get it to his work with no lights
on after a while or with a jump it will run fine. He originally
took it to Autozone down the road and they told him one time
the alternator was good, then it did same thing and he took it back they
took alt off car and tested said it was bad.

200 dollar alternator later, it still did the same thing.
He thought it might be the box under the dash, as he
had problem with all windows working and turn signal
etc. So he got a used one of those boxes from the junkyard
and replaced, now he has all windows, but car still runs down
electrically.

Actually, he traded cars with me a few weeks back, and I drove
the car for like two weeks, only during day mostly, no problems.
I did notice that the right rear turn signal and brake light didn't work,
flashing quickly when turning right, etc, and at one point I hit a big
hole/puddle with the right side tires and the turn signal started working
again.

But he traded me back cars on Monday of this week, and when he
drove it to work in morning same thing happened. He took it to a
small garage near where he works, but they couldn't find anything.
They let it run for a while there to check it and it did run down but they
weren't watching it at that time so they seem to have no idea.

Anybody have any suggestions for me? Help, I need my car back!
:)

There could be some electrical short somewhere.
Check for any loose or rusted wire.
Check out the fuses as well. That should be easy to do.
This are just general tips.More experienced people could give you better advice.

Good luck