I hope you have added some fuel conditioner to your fuel. At -16*, even with the engine running you could end up with a tank full of jelly.
If there isn't a button on the floor to turn the high beams off and on then it would be on the turn signal stalk. I would lean toward the button on the floor.
As far as the emissions light is concerned, I can't think of what would be installed on a bus of that vintage that would be considered an emissions device. Did you change the oil and filters before you left WA? If so, as long as the lube oil is within the safe operation zone I wouldn't be too worried. If it is a big worry stop in one of the truck shops in one of the large truck stops and ask one of the techs if they know anything about the light. Spending a few $$$ for peace of mind can be well worth the expense.