generator coupling and voltage

so my generator quit pumping water, I checked the impeller it was good. decided to go after the coupler, it was bad. while taking this apart I was plugged in to shore power (on the trailer) and was getting a low voltage shock through my body. right hand on wrench and sitting on the motor. I turned the shore power breaker off and it didn't seem as bad but it was present. any thoughts?
Comments
2002 FV 342 on Lake St. Clair - Past Commodore SHC - Vessel Examiner USCGAUX