yo;
Does it have tilt steering wheel?
No Start Troubleshooting; "...
check your upper ignition actuator. Find the ignition rod (on top of the column, running from the steering wheel down to the ignition switch at the base of the column) and make sure it's moving back and forth when you turn the key, through all positions. If it is, your upper actuator is probably not the problem.
check your ignition switch (again, at the base of the column). Manually push the switch back and forth through the different positions. Push it all the way forward (or down) and see if it will engage the starter. If it does, then your ignition rod is probably bent, which can be remedied quite easily. & If it's an auto, try starting in neutral or while pulling up on the lever while it's in park. If that works, look to the Park/NSS/MLPS. If it's a stick, check the clutch switch.
Next,
Between the large posts of your starter relay (it's not a solenoid) should be a smaller post with a wire attached. This is the wire from your ignition switch through the Park/Neutral Safety Switch (NSS)/Manual Lever Position Sensor (MLPS), Or clutch safety switch on a manual trans, or NSS/MLPS with an AOD/E4OD, to the starter relay and the on to the starter solenoid (if equipped) and starter. Check this wire for cracks, open insulation, or anything that could possibly cause an open circuit.
You could try jumping from hot to the small terminal on the starter relay to test it's operation. Sometimes new ones are bad out of the box. If it won't turn over when jumped to the small terminal, you'll know that it's a starter relay issue (Bad part, bad ground or a bad starter. Check to see if da relay is tight to inner fender with no corrosion because the relay's body is ground path via inner fender). If it does turns over jumped to the small terminal, then you'll be looking for something in the small circuit that includes the ignition switch & the park/neutral safety switch (NSS/MLPS) Or clutch safety switch.
There should be 12v running from the ignition switch, thru the NSS/MLPS, to the small terminal on the starter relay. Disconnect the small wire to the starter relay (So it doesn't start by surprise, I'd pull the coil wire too). With someone holding the key in the start position, you should be able to read 12v between any point on that small circuit & ground. When you find where you lose 12v, then you'll know where the issue is...
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This includes all Ign Switch info posted by Bill here for 87-91 including Wiring Diagram, Switch Location & Adjustment, etc.((from Factory manual and the Factory EVTM guide (Electrical, Vacuum Troubleshooting Manual) Source: by Broncobill78 (Dave) at Bronco Zone Forums