Originally Posted by puddinlegs
It's my understanding that if you have a masthead tri-color, you cannot use a stern light on the pushpit. ...
That is correct, in your sailing configuration using a tricolor masthead, you would not use a stern light.
However, as soon as you turn on your engine, you need to turn off the tricolor masthead, and use the normal power vessel running lights (including the stern light on the pulpit) plus the steaming light...