[ray_mcavoy]

A couple possible scenarios come to mind:

(1) There is a wire somewhere under the dash that is rubbing/chafing and intermittently shorting to ground. Going over the rail crossing could have shifted the wire enough to cause it to short out, killing power to the ignition, and getting hot enough to cause the insulation to smoke. From the factory, the main feed wire in these trucks is completely unprotected by a fuse or fusible link. So it would be possible for a momentary short in that wire (or one of the other unfused circuits) to cause something like this. Adding a fusible link to the main feed wire near the battery (like GM did in the 67 & newer trucks) is a good idea to prevent this type of thing from happening.

(2) Does your truck have a factory gauge cluster with a battery gauge? Those gauges are an external shunt type ammeter. Normally, the majority of the current flows through the heavy gauge wire that serves as the shunt and only a small fraction of the current flows through the meter movement itself. However, if there is a poor connection at either end of the shunt (red wire that runs from the positive battery post to the horn relay), it leaves the meter movement (and it's connecting wires) as the only path for current to flow through. And the 64-66 battery gauge wires (black & black with white stripe) are not protected by fuses so they (and the meter movement) will get hot enough to smoke if this happens. I've seen a few of these gauges & wiring burned up from that happening so I always recommend adding a couple of 4 amp inline fuses to those battery gauge wires (just like GM did in the 67 & newer trucks).