I belive the sheild acts as a ground. (simliar to todays coax cable)if its only broken 1/2 way or part thru it will still work.
you can always solder on a small peice of stranded wire to keep continiuity flowing
somtimes you can unravel some of it and make a twist connection and either solder it ot tape it up real tight.
1970 Mach 1 San Jose built Dec 23 1969. Marti says 1 of 7. Purchased in 1987. Original family owner of the powertrain 351C 2v FMX.
1993 GT 11,000 miles, Built 2-12-93 Auto, 3:27 Axle, cloth, sunroof. Untouched except for rubber and battery, Purchased new 8-3-93. still has the factory windshield fluid and new car smell.