Yo,
Welcome!
Re your "ignition switch on top of steering column",
If you replaced the key lock cylinder and not the electrical switch at base of column, then try the IGN Switch Pin-Out Diagram & Continuity Testing (Logic Tables) in 80-91
http://api.viglink.com/api/click?format=go&jsonp=vglnk_146429307409712&key=6ed47b392b9edfe394b9e89b72717104&libId=iooq999o01000bgv000MAbkmxdu9o&loc=http%3A%2F%2Fwww.fullsizebronco.com%2Fforum%2F4194577-post4.html&v=1&out=http%3A%2F%2Fwww.supermotors.net%2Fregistry%2Fmedia%2F831772&ref=https%3A%2F%2Fwww.google.com%2F&title=Ford%20Bronco%20Forum%20-%20View%20Single%20Post%20-%20Bad%20ignition%20switch%3F&txt=http%3A%2F%2Fwww.supermotors.net%2Fregistry%2Fmedia%2F831772
Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
http://broncozone.com/topic/14269-code-reader/?pid=74587&mode=threaded
Some basics;
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.
Run it around to heat the engine up and shift thru all gears including Reverse.
Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Then turn off engine, all accessories/lights (close driver's door) , etc.
Do KOEO test First
Post Code(s) here according to:
KOEO
&
KOER
Dom you think it shuts off when you run over a bump or expansion joint in the road?
If so, Ford does suggest a wiggle test..
Key On Engine Off Wiggle Test Procedure
1.Hook up a STAR Tester, VOM or Scan Tool.
2.Turn the ignition key to the ON position.
3.For STAR Tester or VOM, activate, deactivate and reactivate Self-Test to enter Continuous Monitor Diagnostic Test Mode (DTM). For Scan Tool, enter DTM, then enter wiggle DTM.
4.Tap, move, and wiggle the suspect sensor and/or harness. When a fault is detected, a Continuous Memory DTC will be stored in memory and indicated as follows:
•STAR Tester: Red LED lights and/or continuous tone.
•Malfunction Indicator Lamp (MIL): Lights
•VOM: Needle Sweep
•Transmission Control Indicator Lamp (TCIL)
•Message Center (Continental Only)
•Scan Tool: Continuous Tone
Engine Running Wiggle Test Procedure
Special Note:
•The Engine Running Wiggle Test may be activated any time the engine is running.
1.Hook up a STAR Tester, VOM or Scan Tool as shown.
2.Key off.
3.Start the engine.
4.For STAR Tester or VOM, activate Self-Test, deactivate and reactivate Self-Test to enter Engine Running Continuous Monitor DTM. DO NOT shut the engine off. For Scan Tool, enter DTM, then enter wiggle DTM.
5.Tap, move, and wiggle the suspect sensor and/or harness or drive the vehicle. When a fault is detected, a Continuous Memory DTC will be stored in memory and indicated as follows:
•STAR Tester: Red LED lights and/or continuous tone.
•Malfunction Indicator Lamp (MIL): Lights
•VOM: Needle Sweep
•Transmission Control Indicator Lamp (TCIL)
•Message Center (Continental Only)
•Scan Tool: Beeps
GL!