You should replace everything after the battery connector with high quality connectors and wire. The electronic components installed in almost every starter box are laughable at best. I rewired my starter box with deans wet noodle and a deans plug. I also installed a relay so the current draw was not going through the switch. As far as the sparks in the motor and on the contacts, yes it is normal. Electricity is not the work of wizards, as much as you nitro guys think it is.