You may want to post the KUID of the unit so we can have a closer look. Are you referring to a Mars light or ditch lights? Did this unit work in a lower version? Either way, you might try switching to surveyor, then going to the rolling stock selector and clicking the question mark, then clicking back on the loco. This will bring up the properties of the loco, and there may be options to turn the various lights off and on there. I'm just guessing here, because I don't know which asset that is.