The wires are either for the backup lights or the "neutral safety switch" which is there to prevent starting in gear, probably both. The neutral switch will be at the top of the quadrant, and the reverse switch engages at the bottom.
A good cleanup and lube of the shifter should cure the problem with the mechanical lockout which is necessary to prevent getting reverse engaged while moving forward. Low range ("1-2" on the truck shifter IIRC) should be the last shift position available without lifting up on the shift handle to avoid getting into reverse accidentally. If there is wear or damage to the shift linkage involved, a post in the "parts wanted" forum of this site might get some results.
There is no good reason the truck won't be reliable on a road trip, at least as much as a standard shift vehicle 60 years old, as long as some basic maintenance is done first. Automatic transmissions are smarter than all drivers and most mechanics, as it's impossible to get one in the wrong gear. Most of them have safety circuits to prevent over-revving the engine, even when locked in Low range.
Jerry
