Steve: you nailed it on the relay. Been preaching this on here for ions but few seem to comprehend or remember it.
XB won't start? Always very simple to resolve as per the below...and ALWAYS carry a spare relay and a few fuses. The starter relay is identical to the Key switch and Ignition relays, but unique in the fact that 1 of its internal circuits is used to cut the current flow to the headlight circuitry while activated. That is the circuit that typically causes the starter relay to act up and eventually fail.
Load test battery
Thoroughly clean both battery terminals and both cable ends
Install new starter relay. Crosses over to Ford/Chrysler A/C relays and dirt cheap at all auto parts stores. H-D dealerships have infinite supply in stock.
All THREE XB relays the same part
Crosses over to:
Advance 36126
Napa V11214
Napa V11190
Duralast 19389
Panasonic CM1-D-12V
Harley Davidson 31522-00