What are these (utility?) boxes at the side of the house?
That is non metallic (PVC) electrical conduit.

There must be wires in them that come from or go to the inside of the house to an out building or ?? .

The green cord could be left there for fishing ( pulling ) new wire from one of the  ends. Have you seen this green cord near any other electrical fixtures? 

The covers come off to facilitate fishing the wires, It can be difficult to fish the wires thru many bends, so with this setup, you can pull a length of wire from one direction thru the open body and then pull the remainder as you help feed in to the body to complete the turn, then put the cover back on.