Sorry for the top post.
"Joe" posted this same problem in alt.trucks.ford, insisting
the ignition switch was not the cause, but later admitting
there that he had never checked the switch.
He didn't update alt.autos.ford regarding his mistake so a
lot of time and effort was wasted here trying to help him.
"Joe" wrote: 1997 F-250 Ignition Problem
My ignition switch has always been touchy:
If you turned the key all the way it would not start.
If you snuck up on it slowly it would start.
If you went past a magic point then backed off it would start.
Now absolutely nothing happens when I turn the key.
I don't see anything wrong with the ignition switch.
Substituting a switch from my Explorer did not help.
Any ideas on where to look next? Could I hot wire it?
It sounds exactly like a defective switch.
But you say a known good switch does not help. The
next most probable cause is an intermittent electrical
connection somewhere. Some things to try:
1.) Turn the key while wiggling the gear shift lever. This
may detect a bad transmission interlock switch.
2.) Turn the key while wiggling the wires near the switch
cable. This may detect a broken relay energize wire.
3.) Touch a jumper wire from the 12V battery terminal to
the energize terminal on the starter relay. If the starter
turns this will confirm that the starter is not the problem.
If nothing happens, it could be a bad relay, a bad starter,
or bad battery cable connections.
4.) With a voltmeter, read the voltage at the energize
terminal on the starter relay while turning the key. This
will confirm whether voltage is reaching the relay.
5.) Disconnect the energize wire from the starter relay.
Examine it for a bad terminal crimp (corrosion, soot) and for a
broken wire inside the insulation (soft loose area). Clean the
wire and solenoid terminals and reinstall. Try the key.
6.) Disconnect the switch cable [NOTE-some of the wires are
always hot]. Examine its starter energize wire for a bad
terminal crimp and for a broken wire inside the insulation.
Clean the terminal and reinstall. Try the key.
7.) Take the switch out and operate it manually while reading
an ohmmeter between the switch's 12V battery input terminal
and the starter relay energize terminal. This will confirm if the
switch is okay.
8.) Try another known good switch.
You can rig up a temporary jumper by running a wire from the
battery 12V terminal, to a push-button switch on the dash,
to the energize terminal on the starter relay. To start the
engine, turn the key to the run position and push the button.
Try these things and post the results, with details about each
result (sounds, smells, looks). If these don't work there are
plenty of further things to try.