I think you mean that the core is shorted to the shield (outer braid) in the coax cable. The cable probably has been crushed in the run some where, you will have to follow thw cable to find out where. It will most likely need to have the cable replaced.
This is not Metro specific, as the information applies to all aircraft and radios.
You could try connecting a known good cable ( just make one up and temporarily connect it) and see if the GPS works.