Farkle fitting I found an electrical connector full of corrosion. These Honda ones are small and fiddly to get apart to clean and there is always the danger of bending bits too far.
Looking for an easy clean I found some $2 BBQ cleaner in a spray bottle I had from one of those cheap stores, dollars and cents I think.
Worked well, all the green stuff disappeared. Another spray with a moisture dispersant, then some contact cleaner and all is good.