disengaging parking break = blown fuse

[nictherom]

I keep blowing a fuse on my truck when disengaging parking break noticed a sparking prior to this problem traced the wire back to some little box under my dash next to the steering wheel column. had a previous problem with the throttle cable causing the electrical to blow a fuse. wondering wat to do and what that little box the cable goes to actually does. i have a 72 chevy k10 any help would b greatly appreciated i have work in the mornin and need it fixed asap.