The contact owned a 2021 Ram 5500. The contact stated that the vehicle is a flatbed tow truck, and while one of his drivers was driving at 48 MPH, the tow truck driver noticed that white/gray smoke was emitting from under the hood. It was unknown if the smoke entered the vehicle. The tow truck was towing a vehicle on a flatbed. The contact stated that the driver noticed multiple lights were illuminated, and the RPM was at zero. The driver stated that an abnormal knocking sound could be heard coming from under the front of the tow truck. The driver pulled to the side of the road and immediately exited the vehicle. The tow truck driver used a fire extinguisher to extinguish the fire. None of the air bags deployed. The driver did not sustain any injuries. The contact stated that the damage by the fire was isolated to one side of the engine, by the heater of the relay intake on the driver side. The wires that were connected to the relay were damaged. The fire department was called. The police were called and arrived after the fire was extinguished. It was unknown if a police report was filed. The vehicle was towed to the business location. The contact owns a vehicle electrical shop and determined that the fire was electrical. There was no damage to the vehicle that was towed. The vehicle was not taken to the dealer or an independent mechanic. The insurance company was not notified. Â The manufacturer was not notified of the failure. The failure mileage was 189,040.