Nissan Repair: Loss of Power to my 96 Nissam Maxima, rental car company, nissam maxima

Question
When I turn the ignition, everything dies.  Originally, I would lose all power whenever I stepped on the brake pedal (but only when the emergency brake was up and the car was in park).  The car was a repo and from teh body damage I can tell its been in at least 2 accidents.  Also, apparently previously owned by a rental car company in Las Vegas, so there's really no telling what's been done to it, but no one can figure out what my problem is.  I've taken it to 3 separate Nissan dealers, to Firsestone and to 2 private auto repair shops, but of course, the car worked perfectly the entire time they all had it.  Two of the Nissan dealerships took the opportunity to charge me for work I'm now sure it didn't need.  One replaced the starter, another replaced the battery cables, the third was honest enough to tell me that they couldn't find anything wrong, but it never fails...  A day or two after I get the car back, the problem starts again.  When it was reposessed, they gained access to the car through the trunk and broke the trunk lock, so I figured it must be an electric problem.  The pre-sets on the radio are cleared everytime I turn off the ingnition, so that too lead me to believe the problem was electric.  One of the private repair shops I took it to specializes in electric problems and they couldn't find anything wrong either.  I let the car sit for over a year because I was tired of sinking money into it, but I don't want to junk it, because it still runs great (when it runs that is).  I know it's difficult (if not impossible) to say what they problem is just by what I've given you, but have your ever heard of anything similar before?

Answer
It sounds like to me you have a bear wiring rubbing on metal shorting out your system,

it could be at
your radio
on a tailight, headlight, as far as a wire being bare on the motor (due to the accident)

This will take time and effort to tract done each wire, you have to tract down the wires from end to end.  

It could be a bare wire under the dashboard.

The reason why I say bare wire is becuase of the inconsistance of loss of power.  If there is a bare wire and it is touching on/off then that is why you get the inconsistancy.

Also Check the ignition, there is a main wire that runs from the ignition that wire sends a signal to tell it to start to turn over.

If that wire is damaged (the rubber) if it is touching something bare it is shorting it out.

This specific wire is what companies use to wire in stereos and car alarms.