yo JIB.
R&R key lock cylinder; pull lock cylinder out and replace it with another one from a yard queen or buy new.
Lock Cylinder & Switch Replacement & Depictions in 87-91 (figure 1) (from Factory Manual and the Ford Electrical & Vacuum Troubleshooting Manual (EVTM)
Source: by Broncobill78 (Dave) at Ford Bronco Zone Forums
Bill wrote, "Here's everything from both the Factory manual and the Factory EVTM guide (electrical, vacuum troubleshooting guide) about the 87-91 Bronco ignition switch. If you're having ignition problems and suspect the ignition switch,
lock cylinder or actuator rod then this is pretty much everything that Ford ever published about it. Hopefully this will help you solve any switch related issues that crop up and if nothing else it's good info to save & print for a rainy day."
http://broncozone.com/topic/14120-87-91-ignition-switch-info-troubleshooting-guide/
&
just in case,
Ignition Switch Adjustment Proceedure & Switch Pin-Out Diagram & Continuity Testing (Logic Tables) in an 83; "...The following proceedure is from the 1983 Ford Service manual, with a few minor wording changes, but should work for any year. Also included are a couple of illustrations from the same proceedure to help you visualize it..."
Source: by Seabronc (Rosie, Fred W) at Ford Bronco Zone Forums
http://broncozone.com/topic/7243-ignition-switch-adjustment-proceedure/