Hmm. I'd need to check further, but by this period, the VHF radios should have been fitted, so the wire would have been removed. The 'give away', such as it is, is the antenna mast, being the later, 'profiled' version, enclosing the carbon rod antenna itself. Behind this is the antenna wire insulated 'lead in', which was retained, but not connected to the transmitter/receiver.
When the bulged, 'Malcolm' hood was retro-fitted, the 'mast' and insulator were removed, and replaced by a 'whip' antenna, further aft, off-set to starboard.
On earlier P-51Bs, the original (HF) antenna wire fed from the 'tubular' mast, and then was moved to the insulator position after up-rated sets were installed, before the change to VHF, which initially utilised the 'old' style mast, as can be seen in this well-known shot of Don Gentille's aircraft - note the lack of wire connection at the insulator, and this was in March 1944. (shots from other angles, taken at the same time, clearly show a lack of fin connection also, as do many 'period' shots of other P-51B/C aircraft).
However, it's possible that a HF 'Command' set was retained, in addition to the VHF set, which would require the antenna wire, and maybe Bill could possibly clarify this ?