cant seem to figure it out

[apacheclay]

i have a yamaha g22 that isnt charging ive tried the generator test by jumping the green wire to ground and it reads over 15 v at the batt checked tomake sure the voltage reg had ground on the black wire made sure that the red and white wire had 12 volts at the generator so i thouth it was the reg bouth a new one and the problem persist now what i notised is that when i groung the grenn wire on the gen it wont start but if i start running and i ground it it will read the 15 volts any ideas and by the way when i om test between the green wire and the red wire on the gen it reads 7.8 not 5 like ive read some. any help will be greatly apreciated

[apacheclay]

anyone ?