I installed a new garbarge disposal and it had a plug on it. I have no outlet under the sink so I put a grounding plug on the power wires. The disposal worked fine for a month; then no power to the disposal. (I used an extension cord and the disposal works fine.) I replaced the plug and it worked today. No power tonight. Circuit breaker not tripped. The disposal and sink light are in the same switch box. Light switch is fine. Could it be a problem with the disposal switch?

How did you " put a grounding plug on the power wires "? It could be the outlet, switch, a GFCI, or a loose connection...