Legal to drive here in the daytime without trailer lights if you can see the ones on the vehicle.
You could just put one of those orange triangle things on the back an call it done. Seems quite popular to do around here even not on hay wagons.
Sometimes you can hack into the vehicle wiring, but more often you need the converter anyway. Most cars have separate blinker and brake lights, trailers use the same bulb for blink and break.