Abandoned lamp post wire causing breaker to trip
A fundamental rule of electrical installation is that every wire must terminate in a junction box that is accessible without taking apart any part of the building (obviously other than the junction box cover, receptacle, switch, lamp etc. which covers the junction box).  

So you have to search.  Unfortunately the mere fact that a junction box has a live wire in it does not mean your wires aren't there.  Yours could be "passing through".  But if a box is inexplicably dead, it is certainly part of that circuit.  Follow the wires and/or follow your nose.  

Another rule of electrical installation is that wires have two ends, and if you unhook one end, you must unhook the other end too.  They should have done that for you, to avoid this problem...