Yes park is always tail light only on.
Yes black is powered to key on.
Are all your wires plugged in in the headlight bucket?
Yes on a 77 550 the head, front marker and tail lights should be coming on with the key in the on position.
Is there something you haven't told us about on your bike?
Is the bike wiring 100% original from the factory?
New harness?
Switches?
Custom made harness like for m-unit?
Relays added into the light circuits?(there weren't any originally but could have been added like Hondaman makes up)