As many have replied different states will have diffrent rules and/or levels of enforcement.
Personally I towed a dolly for many years with only the dolly lights. Then one night going through Virginia I was stopped for not having any rear lights. Fortunately my pleas of stupiity worked and I was not cited. I did turn on the parking llights when I left to satisfy the officer and found a Wal-Mart to purchase magnetic lights as soon as possible.
Bottom line we will all do what ever we are comfortable with until someone changes our mind.