What should you do when a law enforcement officer is directing traffic?

I believe the answer is: wait till he signals you to go

A law enforcement is assigned to direct a traffic if either there is an error in the traffic light system, or  the road is really packed to the point where traffic lights could no longer be able to clear it.
If the traffic lights are still functioning together with the officer, you need to completely ignore the traffic lights and prioritize the officers' direction.