I've kitbashed an Athearn NW switcher into a box cab. There really wasn't enough room left to put a reasonable size speaker in it, so I built a follow-along oil tender that contains a sound-only decoder, the speaker, and a motor decoder set up to control only the backup light.
Electerical pickup is by way of four pieces of brass wire picking up power, either from the back side of the insulated wheels, or the axle of the wheel set. This seems to work well for the sound decoder (it has a keep-alive capacitor) but does not work well for the backup light. The light flickers whenever I move the car. It stays nice and steady just sitting on the track. I have checked all my solder connections and all seems OK.
Is there a capacitor or something I can add to the circuit between the decoder and the lamp that would keep the lamp steady?