I have owned my 1985 short box 4x4 for about 10 years now. Decided it was time to freshen it up a little and add fix some issues. One issue is I have never started this pickup with a key. Mounted to the lower dash is a black plastic case that contains a switch with a twist knob. The knob has all the functions a key style ignition has and plugs into the factory harness. On the case there is a number and a pentastar logo. Is this thing factory? Aftermarket add on? Don't know how to post pics and forgot to get the number off of the piece.

I've never seen what you described but pics and more info would certainly be helpful.

Posting pics has been detailed on these pages dozens of times. Look in the forum help section.