OK, so I'm going to quickly prove that I'm not an electrician.
I was told that the Leviton switch for my light / disposal was obsolete and finding a plate would be difficult, so I opted to replace it.
I turned off the power, put in the toggle, then turned the power back on and flipped the switch (using insultated pliers). There was a big flash and sparks shot out, then it died. I went downstairs and saw that two circuits had tripped.
OK, so that explained why I had two black wires. I then found out that one of the blacks went to a circuit for my dishwasher and the other was a different circuit. I removed the dishwasher circuit wire from the toggle and hooked it up so that the garbage disposal and the light are on the same circuit. I capped and taped the other black wire.
Last night i noticed some funny things. The dishwasher made new sounds. The cordless phone charger station died. And the light can take a moment or two before it turns on.
Did I kill the switch or the gear?