I don't think you want to use the headlight (white wire) and rear light (yellow) for your yard and roundhouse lights. These are tied to the forward and reverse direction of the locomotive. Both usually can't be on at the same time and as you change direction of your turntable the lights will switch on an off.
For you yard and roundhouse lights, unless you feel compelled to control them with DCC, just wire them up to a switch.
Wiring For DCC