A lit indicator shows something about that switch or accessory, but it does not prove that the motor is receiving a correct supply. Its meaning depends on how the control was designed and connected.
What the observation tells you
Do not use the light to rule out an electrical fault or to justify opening the appliance. Record whether it changes when the normal control is operated and whether the disposer is silent, humming or functioning, using observations already made rather than repeated trials.
A useful next step
Give the engineer the control's identity as well as the disposer model. The two may be separate products with separate documentation.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.