Your game was working correctly before you cleaned it. It is designed to be turned on by the left flipper (or pressing the replay button or inserting a coin). "Sparks at the outlet" is a little scary - I hope that means just a small arc to a prong as it is plugged in, and not actual emission of sparks like a welding operation (if so, call a professional electrician now!). I think what you have done during your cleaning operation, is maybe closed the replay button switch or one of the coin switches somehow. That will both power up the machine and energize the replay unit reset circuit continuously when you plug it in.

Also, if it already doesn't have one, put a 3-prong (grounded) plug in it ASAP.