You can find shorts in outdoor lighting by looking for wires that are cut, broken, frayed, are improperly connected, or are stretched by roots or rocks. Also look for bad, wet, corroded, or damaged sockets. Check for any areas that are exposing the wires or bulbs to moisture too.
A short in lighting is when electricity is going where it isn’t supposed to and nothing is slowing it down. What makes it so hard to troubleshoot is it can happen in many places at the same time.
If you can’t find the cause it may be best to contact an electrician
Jack isn’t about to look over the whole system in the dark, even with a flashlight, so he moves on to the next possible issue.