Check for a short circuit with an ohm meter if you have one. Make sure there is no voltage with a volt meter first. I just use a digital multi meter. Do you have a garbage disposal ? Could have corroded through, mine did that a few years ago. You most likely have a short or an arcing somewhere. I hope it isn't a rodent problem. Somebody thought it would be "green" to make insulation plastic from soy beans.
Sometimes it helps to draw a wiring diagram or schematic.