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?
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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)