The previous owner probably hooked it up incorrectly. I would assume that the radio draws power from the "on" and "acc" position. When I installed my stereo I didn't have to trace the wires back that far since I just used the stock red power wire.
I'll take a look at some schematics and see if I can help you out.
Bronco Info: '83 VIN & title on '93 frame/body w/'95 4.9L & EB paint
Go to the Tech Writeups forum & read the thread about "ignition actuators". Read the TSB about the ignition switch recall. Find an old Haynes manual with a red cover (eBay?) & use the logic table in the last chapter to test your ignition switch.
I have a similar problem but when I hook up the green/black cable to a power source and have my interior light nob on the interior lights turn on. And my stereo doesn't save any settings I do to it. Any ideas.?
Lock Cylinder Adjustment & 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-ign...nt-proceedure/
Switch Pin-Out Diagram & Continuity Testing (Logic Tables in 87-91 (from Factory Manual and the Ford Electrical & Vacuum Troubleshooting Manual (EVTM)
Source: by Broncobill78 (Dave) at Ford Bronco Zone Forums
see attachmt. below
See note- the 37 & 297 Pairs are connected together internally in sw.