85TC. General question. (relay?)

[adamsnez2]

Hi, first time poster. This is an easy question but im not sure of it myself.

Passenger side, underneath the glove box. There is the floor light that is connected to the underside of dash, and a black plastic box next to it (few inches high, by a few inches wide it is).
What is this box, and what is it's function?

While i was installing my cd player in the glove box, some metal on this box hit a metal crossbar behind the glove box and sparked. Now i would like to know the importance of this box. THanks.