Motorcycle Questions? Ask a Mechanic.
Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, proposed preliminary try (if have not been tried) would be to re-check / swap how/where the big cables are tied to which terminal of the starter relay/solenoid.
Or perhaps you can provide a clear close up picture(s) of the starter relay's terminals.
All others would require the use of a volt/multi-meter and a check of the wiring, resistance/continuity and voltages.