Note that, when the VHF radios were fitted to the P-51D and P-47 ( and up-dated P-51B/C models) operating from the UK ( and later mainland Europe) with 8th USAAF, the wire was not fitted, the antenna being in the "blade" mast, or, on Bubble-hood P-47, and Malcolm hood P-51, in the form of a "whip" antenna on the mid fuselage.
Where some P-51D's previously had the wire, the "lead in" opening in the rear of the canopy was covered over, normally with clear Perspex.
The earlier P-51 "razorbacks" which had originally been fitted with the straight, tubular radio mast and the wire to the fin, had the mast replaced by the "blade" type, and the wire removed, if still using the framed canopy hood, when VHF radios were retrofitted. If a Malcolm hood was fitted, then the "whip" antenna was used.