Reattach the electrical wires. Unscrew the faceplate on the underside of the new unit. Match the colored wires on the power supply to those in the disposal’s electric housing and connect them using plastic wire nuts. Slip the copper grounding wire over the green screw at the far edge of the compartment. Replace the cover and tighten the screws.[16]
Hold a noncontact voltage detector against the wall switch with the switch in the on position. The presence of electricity at the switch causes the detector to beep and flash. Leave the switch in the on position and hold the detector against the outlet beneath the sink. If the detector does not sense the presence of electricity at the outlet, the switch may have failed and electricity can no longer reach the disposal motor. Have the wall switch replaced.
Another common cause for a leaking garbage disposal is the disposal flange. A leak at the very most upper area of the garbage disposal could be the garbage disposal flange which goes through the sink. A garbage disposal flange should be sealed with Plumber’s putty and then tightened from underneath the sink. If this is not tight enough or if it has managed to come loose (which can happen) then the garbage disposal will have to be taken down so the flange can be resealed and then the garbage disposal can be rehung.

Garbage Disposal