1999 Cadillac Seville electrical system problems

My son almost died on october 25, 2013 in his 1999 cadillac seville in our driveway while he was relaxing in it with his dog. He had fallen asleep waiting for his mother/my wife and the engine caught fire. He needed to climb out of window and pull his dog through the window. He injured himself and went to hospital. The fire was so intense that the engine fell apart from heat, the cabin was destroyed, front tires are gone/melted while trunk and gas tank were relatively fine.

When I drive at any speed randomly the gas gauge goes to empty,windows don't work, AC goes off but fan still blows, power locks don't work, lights stay on when I stop and get out, but when I put the key back in and turn it to the "on" position and back off everything works again my battery went dead a few times due to the lights staying on and my girlfriend not knowing what's going on...what is that!!!!!