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, let's review the basics...
Inspect the battery, its ground lines and/or check/clean the battery cables + terminals, connectors and wiring as a preliminary consideration. Have the battery externally charged and then LOAD TESTed (even if new/charged and just for the purpose of eliminating it as a suspect).
Particular attention to all black wires including those tied to the battery's - terminal, harness to frame and engine ground.
Additionally, consider to hardwire a secondary ground line from the battery's - terminal to the engine. frame and harness' black wire(s).
With a volt/multi-meter, determine the battery voltage when: