Electrical Issues!!!HELP

[52MercRR]

My son has a '72 C10 SWB. The dash, brake and tail lights quit working. I printed off the electrical diagrams from this site(Thanks). I have no power on the fuse block upper right fuse. This looks to come from the connector for the dash assembly(gray wire). What I can't tell is where this power originates from. I can't find anything that tells me how circuits are switched. The drawings show multiple wires from the light switch, but not how they are controlled through the switch, i.e. N.O., N.C., which wire connects to which at each detent of the switch when activated. Can anyone shed some light on this issue? Any thoughts are appreciated. Thanks.