Why not cook marshmallows on my under dash fire?

These things are buss bars. The one marked covers 3 fused branches ( although the end one wasn't used ). One of the 3 male spades on the bar must have a supply wire or none of the branches will receive any power. So there's a 3 branch that is hot in run, a 2 branch that is hot at all times, and a single that is hot from the headlight switch park lamp circuit.
Anyway... You wont find many "extra" wires in older cars.