Hi Simon...
Wiring issues always so hard to put into words! Furthermore I don't have a '500.... but am assuming most Hondas abouts that era were wired roughly the same.... so have included a CB400F diagram.
As I read it, a live comes from the flasher unit into the handlebar switch. Depending upon your L/R selection on said switch, this live feed then exits via the Orange OR Light Blue wire to the respective indicators... through them... and down to earth, completing the circuit.
Let's assume you make a LEFT selection....
Black live into flasher unit....(white?) out to handlebar switch.... now out via Orange wire to both Front & Rear LEFT indicator lamps. From here through the bulbs... and to earth.. L indicators flashing.
This orange switch feed ALSO goes directly to the pilot lamp, through it, now out through the LIGHT BLUE to the R indicators... through those bulbs & to earth. The indicator lamp now also flashes.
BUT, because it is only 2 Watts, versus the indicators combined 36W, it flashes.... the indicator bulbs - as far as the weeny pilot lamp is concerned - may as well be a fat earthing wire.
And when you indicate in the other direction, the pilot lamp circuit is simply reversed, but with the same outcome.
I guess the proof of the pudding would be to remove the two (R) indicator lamps & select a Left turn. The L flashers should work normally, the pilot lamp.... denied of its earth... would not.
I hope I understood your question, otherwise apologies.
Simon.