How to find where is the broken in the house electric wire?
My most valuable tool is thinking about what the last guy did.  Or was most likely to have done.  I see lots of "what were you thinking?" situations but later I learn something else, and go "Oh, that's what he was thinking." 

OK the wire goes through the cement wall. Somebody had to install that wire the first time. Where would he have routed it?  What would've been easiest for him?  

Do you have more than one outside light?  Is it possible this light is fed from one of the others?