It maybe a loose/bad/frayed wire or corroded connection that might be the reason...use some electrical contact cleaner & clean the starter solenoid/main harness connection/30 amp fuse...Hi. I checked all thee contacts and it looks like they are showing proper voltage. Also switched back and forth between old and new rectifiers but no see no difference.
& also clean the starter button/light switch & on/off..!!
Like this... https://www.ebay.com/itm/Electric-Contact-Cleaner-Spray-WD-40-Specialist-Electric-Equipment-Cleaning/233257555992?hash=item364f3bd818:g:8L0AAOSwA6ZdA7cC