I drive a '78 Bronco 400 w/auto trans

It turns, but won't fire over.

Last friday, I went to drive home from work, so I go to turn the key and smell something electrical burning. I even think I see a cloud of smoke come from under the dash board.

I checked my fuses under the dash, fine. I've checked my plugs, even done a spark test. I've checked everything around the selinoid and accompanying fusible links, fine. I've checked all the vaccume lines in the engine compartment, fine.

A friend at work told me about the actual wire harness that goes to the ignition switch. He said sometimes they burn out. I have a spare ignition switch I can swap out, but has anyone heard of this. I haven't checked any relays. Any thoughts anyone?