First check would be that the lower sealed beams are good. They only come on when high beams are selected. They use just 2 terminals (50 watts). To test, just use a battery charger.
If they're okay, check the front lighting ground points.
Left:
You must be registered for see images attach
Right:
You must be registered for see images attach
Next, I would pull the H/L dimmer switch (hi-Lo beam switch) and check it for operation.
You seem to already know the operation of the two different sets of H/L's. But if somebody else doesn't, it goes like this:
Low beams selected - Bottoms off. Only low output filament (35 watt) of top sealed beam is energized.
High beams selected - Bottoms come on (50 watts). Low output filament of top lamp is turned off - high output (50 watt) is turned on.
These images explain better.
Low beams:
You must be registered for see images attach
High beams:
You must be registered for see images attach