Can the switch for a kitchen sink disposal be in the cabinet under the sink? When you open the cabinet door it is within reach. This is in the state of Arizona. Also does the furnace need to be pluged (or hot wired) into a fused switch?

Thank you in advance

Sure, a disconnecting means only needs to be accessible to an appliance for servicing purposes.

Not exactly sure what you mean about the furnace. Most, if not all furnaces, are wired with at least one circuit, back to a circuit breaker in a panelboard.

There may be local codes that require disconnect switches in certain locations for certain furnaces. At least one switch is usually located at or on the unit to serve as the required servicing disconnecting means.

Don't know of violation of code.
One time, I place a Decora switch in little tilt out door under sink. You had to open to turn on. You could turn off at switch, closing door also turned off.
Used small clear rubber bumper, so door closing turns off switch.
Kind of a safety feature, If you lean over like a kid might do, it shuts off.