Doesn't matter, the wire runs from the lamps, to the MFS, nothing in there expect a splice or two. Wire should be zero resistance, regardless of switch positions.

 

there is a red / orange wire in the MFS plug, but it is a larger gauge, so I’m not sure this wire runs from the plug to the switch. At any rate, there is no continuity from end to end.

 

Wire is broke somewhere. Both high beams use the same wire, so, likely, it's small gauge at the connectors, going to a larger gauge at the splice. Gonna have to trace them down to find the break.

 

so based on the simplicity of it, I should be able to run a new wire from the MFS plug to the bulb plug and be back in business, right?

 

Correct that's called an overlay. I would back probe the wire at the switch (just stick it in) run it outside to the connector (again shoving it into the back) to see if the work. If they do run it next to the factory harness.