Generally a sprinkler system is designed to operate 4-6 sprinkler heads
at a time. This number is dependent on the type of heads and the water
pressure available. If you were to turn on all of the zones at one
time, the system will not distribute the water properly due to low
water pressure.

If you do not have the manual or cannot figure out the number of zones
or the number of heads, I would contact a sprinkler contractor. I am
sure that they would stop out without charging you to give you a run
through.... it could be future business for them if you should need
service down the line.