Mitsubishi Repair: alternator dead? fusable link? blown fuse/relay?, eclipse gsx, blown fuse

Question
I own a 91 Eclipse GSX and recently removed both the upper and lower exhaust manifold heat shields in order to find where an exhaust leak was coming from.  While working the lower shield up and out, I accidently contacted the alternator with it while doing so and it sparked(arced?) against the exhaust manifold. I realize it was dumb to work on the car with the positive battery terminal still on, but thought I would be far enough away from electrical and fuel components to be safe.
It started up and as I drove home on the freeway It seemed to run fine. When I off the freeway into slow and stop and go traffic, I noticed my lights dimming(both interior and exterior) and then my radio died, and just as I pulled up at the house the rest of the car died as well.
the 80 amp alt fuse looked intact.  I checked the battery with a volt meter the next day and it was back up to 12, but wouldnt start, so I got a jump, pulled the jump cables off and checked the voltage on the battery again and saw that it was rapidly falling.
Swapped batteries and checked again, It didnt fall as rapidly as my already drained batt but only read 12(instead of 13+) volts while running
A friend suggested that it may be the fusable link that went out(I dont know what that is). I dont know how to check the relay either.  Another friend said the battery may have ruptured a cell and wouldnt take a charge even if the alternator worked.....or that some combination of all of the above was possible.
I would appreciate any help you could give me, thank you.

Answer
Chris,
You need to replace your alternator.  Shorting out the alternator with exhaust shield most likely blew the voltage regulator and/or diode within the alternator.  You mentioned all the signs of a malfuinctioning alternator; only seeing 12V at the battery with the car running, dimming lights, and dying radio.  

Have the alternator replaced, and you should be back to normal. Also, driving around with a faulty alternator puts an incredible strain on your battery and will soon kill it all together.  Have your battery load tested after replacing your alternator to be sure it can hold a complete charge.   And if your battery is around 5-7 years old, it's probably ready to be replaced soon anyway.
Good luck!