Came out to perform preventative maintenance on furnace. Met customer at garage and began to discuss the maintenance being done, filters, and any questions regarding the service. Customer stated that the filters were changed recently, and that the system seems to be doing well. I inspected the ductwork, blower assembly, motor, capacitor, electrical components, heating components, evaporator coil, heat exchanger and overall condition of equipment. Blower assembly will need to be cleaned soon. Cleaned flame sensor and dust off the burners and components. Checked system operation, amps, temperatures, gas pressure and CO levels. Found the receptacle and plug charred and in need of replacement before it trips a breaker, or something happens electrically. Showed customer photos and they approved repairs. Shut breaker off and replaced the receptacle and furnace plug. Cycled system back on to recheck operation system is heating properly at this time.