Electrical Circuit in jack compartment?

Can someone tell me what the electrical circuit is that is in the jack compartment under the rear storage compartment in my '81? I haven't looked in a while, but it is on a printed curcuit board about 2" x 3" and has around 6 - 8 wires going into it.

Also, mine is just haging there. Can you describe how it is supposed to be fastened?
Thanks!