A sail boat under power, is a power boat. meaning they have have to follow the same rules. As far as I remember, as long as the motor is running, they are under power. The term "sailing vessel" means any vessel under sail provided that propelling machinery, if fitted, is not being used.
So, if under power, should have the same nav lights.
red / green sidelights
masthead
stern
Here's USCG info on the forward apex.
https://www.navcen.uscg.gov/?pageName=Rule25
e) A vessel proceeding under sail when also being propelled by machinery shall exhibit forward where it can best be seen a conical shape, apex downwards. A vessel of less than 12 meters in length is not required to exhibit this shape, but may do so. [Inld]