Headlight problem

[Yukon Jack]

A buddy is having a problem getting his headlights to work. If he just pulls the light switch halfway out, to the parklight position, the parklights come on and the blinkers all work. If he pulls the light switch all the way out, no park lights and no headlights but he does have tail lights. Bottom line, everything works except the park lights and headlights with the switch fully on. Tony got his tester out and it doesn't appear that he is getting juice to the headlights but it doesn't make sense why the park lights work with the switch half way out but not with it all the way out. There's one wire plug that comes out of the harness and goes through the front radiator support that connects to the headlight assembly. He has no juice to it as far as he can tell. The park lights feed from a different wire, from a different wire harness. He is baffled as he has put in three different light switches in the truck and they all act the same, no headlights or park lights with the switch in the full out position.

Any thoughts?