I am considering building a train that uses a 12v motor from the 1980s and Power Functions LED lighting. For this to work it would be necessary to run the Power Functions LED set from one of the 12v sockets on the motor.
Obviously the physical connection is not compatible, but it should be straightforward to remove the connector brick from a Power Functions cable and fit 12v-style plugs instead. Where I'd welcome information is the electrical aspect. Since the LEDs are designed for 9v, exposing them to 12v may damage them, and they will need a resistor in series to reduce the voltage across the LED set to 9v.
Has anyone determined the correct value of the resistor? Or the current that the LED set draws at 9v, which would allow the necessary resistance to be calculated using Ohm's Law.