If I understand correctly what you are asking for, then a 'DCC 8 pin blanking plug' is probably the simplest option. This comes in the 8 pin socket of RTR locos supplied 'DCC ready' so that they will run on DC.
But with the blanking plug inserted, when given DC power not only will whatever lights are fitted light up, (direction dependent of course as applicable) but the motor will also run. If you only want the lights to work, then either chop off one of the motor supply pins (pin 1 orange wire, pin 2 grey wire) or disconnect / cut a motor supply wire, your choice.
But with the blanking plug inserted, when given DC power not only will whatever lights are fitted light up, (direction dependent of course as applicable) but the motor will also run. If you only want the lights to work, then either chop off one of the motor supply pins (pin 1 orange wire, pin 2 grey wire) or disconnect / cut a motor supply wire, your choice.