Go with the recommendations in the Harley manual. Adjust for your load (weight of you, your rider and baggage -- don"t be lazy about adjusting for different loads).
The number on the sidewall is MAX pressure the tire is rated for--the "do not exceed' pressure. That spec is determined by the tire manufacturer. However, when the tire leaves the tire factory, they don't know what motorcycle it's going to end up on. Therefore, the motorcycle manufacturer's spec trumps the number on the tire sidewall. BTW, the same principle applies to tires for cages, too.
Check pressures often--you only have 2 contact patches and unlike 4-wheelers, you lean on them
Good question--lots of confusion out there about that.
"Borne on the steel breeze"
2004 Road King FLHRI