What could cause total electrical failure on a 1992 ford astrovan?

I recently brought my 1992 ford astrovan to a stop. When I applied the brakes and shifted the tranny into park before I could turn the ignition off with the key the motor died and I lost all electrical power to anything. Nothing electrical worked. I lifted the hood and began a visual inspection. First thought was maybe a loose battery terminal. I noticed the positive terminal was extremely corroded, however both terminals were very secure. As I continued my visual inspection I witness a spark and a "sizzle" sound right on top of the positive battery post. I stepped back and just watched a second and it happened again., an arc between the positive post and the terminal. I thought best at this time to unhook the battery from the circuit. I ran into the conveinant store to borrow a wrench for I was without, and when I returned my girlfriend informed me that it arced a couple more times in my absence. I removed the terminals and cleaned all the corrosion the best I could and attempted to put the battery back in line and the second I connected the positive cable the arcing began again. Still no power to anything.

Well a little sandpaper or wire brush is the best way to clean the corrosion off the terminal. But you may have another problem. Arcing is unusual. There should not be that large of a draw. So you need to do a visual inspection. For example, the battery + cable always goes to the starter + first. Since the starter is on the engine, it rocks back and forth as you accelerate, and it also has an exhaust manifold hot enough to melt insulation. So check if the battery wire is shorting on something.
If that is not the problem, then leave the + battery terminal off, and put a test light across the battery.
If it does not light bright, then the battery at least needs to be taken out and recharged. Don't try to jump start it, because if you do get it started, not only could you still have a short, but the alternator will burn up trying to charge a totally dead battery. After charging, put 1 battery cable on, but put the test light between the last terminal and its post. It should not light brightly, even though it is bright if across the 2 batter posts. If it is bright, then something is on and draining, and you have to discover it by removing things 1 at a time.

Youve got a dead short if i got this right you shifted to park and it died my choice would be the neutral safety sw. Shorted

Clean the posts and cables.

When the engine is running, the alternator supplies the electrical power needed to power the ignition, lights, etc. If the engine stopped with the key on, something else is happening. Arcing only happens when there's current or a "load" on the battery like lights or a hard short meaning a direct path from the positive terminal to the frame (negative terminal) which could have lowered the voltage enough to kill the ignition. Fuses and breakers normally prevent that. Take the battery out. Use an ohm meter to measure the resistance from the positive to negative battery terminals. With everything OFF (dome light, ignition key, security system, engine compartment light, etc) you should see very high resistance. If you read very low or zero, don't connect a battery. Shorted alternator diodes can short the battery to ground. Disconnect the fat cable at the alternator and check resistance at battery cables again. If the vehicle was involved in an accident, wiring may be shorting out where the body is damaged.