1995 Firebird V8 6speed

I just put a new engine in my car and every time I go Threw a puddle or it rains the car will stall and then will not start until it dries out. Can Someone give me some advise. I'm not sure if I should bring it back to the mechanic and tell hime to figure it out since I paid him good money to intall the new engine or not.

I would definately take it back since soemthings wrong. Sounds like a exposed battery cable or ground strap.