Almost surely powering something with 12V. Maybe a camping mod for lighting or tailgating for TV, cell phone charger, or electric cooler as was also suggested.
Either way, that mod looks very sketchy to me. Lots of crimps and electric tape. If you are not comfortable removing it yourself, get some professional help. I do not recommend just cutting the wires off in the bed. If you got sparks on the last try, you may now have a blown fuse somewhere.