Newman Atkinson says:

One thing would be to change the light bulbs. If they are LED then most likely there is a resister that you might change for a different resistance on each LED Bulb. There may also be a CV in the settings that might adjust them but not for sure. If you have resisters with regular bulbs then that might be a consideration although without the resisters in DCC the regular bulbs can shorten their life over regular DC power. Also check the wiring to the bulbs they may have used a case ground for the bulbs especially if it was wired by someone new. With DCC you need both the white and yellow wires and the blue common ground wire and if the bulbs are grounded to the frame through the old light mount then isolate that ground and use the blue wire for ground of the bulb.
from Newman