When I was new to the hobby, I learned this the hard way. I had just acquired a heavily routed WhirlWind that had a couple of wires that had come off a few of the solenoids; unfortuantely, I did not notice the overfusing. I reconnected and literally had flames shooting out of the back box. Since then I have learned to check the fuses, as well as solenoids before powering on a game, and learned a ton rebuilding that machine.