its not a defroster... its a toaster oven...

 

That hole in the tranny is plugged using a rubber boot. I ran mine without one for a while with no problems. You should be able to pick one up at the dealer pretty cheap.

As for the black box - maybe the Flux Capacitor?

 

Does your D2 have front windshield defroster? Look in the recess below the windshield when the hood is open and see if you have a plug and wires in both the left and right recess.

 

Hey, you stole my answer!!
I too was going to say heated windshield.