make sure the battery wires have clean tight connections. Also the 2 battery wires have to be of substantial size. too small of wiring will cause resistance which causes heat which melts wiring. did you change the wire running to the solenoid? sounds to me like a loose connection somewhere, either on the pos or neg wire. also the battery should last for years not months. http://www.briggsandstratton.com/ has a wiring diagram.