I have 6 of these engines and 5 of them have decoders installed. I have never had any trouble with the light boards working with out any modifications. I have digitrax zephyr controller and the "0" key turns the light on and off.
Try that first if that dont work you might want to check your connections in the soldering. Worse case detach the light board from the decoder and try powering it by sticking the wires to the rails. This should make it work just like it did on DC. If it dont work you have a bad LED and would need to order a light board from bachmann.
Try that first if that dont work you might want to check your connections in the soldering. Worse case detach the light board from the decoder and try powering it by sticking the wires to the rails. This should make it work just like it did on DC. If it dont work you have a bad LED and would need to order a light board from bachmann.