SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

We just purchased a home from an elderly man. We just found 2 sprinkler heads that say Rainbird 15103. They are round black plastic things in the ground. The previous owner knows nothing about them. So we are assuming we have or had a sprinkler system. How do we go about finding the controls for it? We cannot find any type of timer system or any water faucet nearby. Where should we start looking for the controls or where it connects to the rest of the water pipes? We are at a loss. Thanks! Peke