When traffic control lights are NOT working, you must _________ before proceeding.

Explanation

If you approach an intersection at which the traffic lights are not working, you should treat the intersection like an all-way stop (i.e., as if there were a stop sign at each approach to the intersection). That is, you should come to a complete stop, yield the right-of-way according to the rules for all-way stops, and then proceed (with extreme caution) when it is safe to do so.