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No. The 1966 alternator harness has a lead for the ammeter, so it's not compatible with the 65GT version. All other 65's use alternator indicator lamps, which require different wiring for the VR (and presumably) for the alternator.
Regarding the only alternator wiring harness itself. The 1965 alternator wiring harness has contains an extra connector (near red cap) for the "External Radio Interference Suppression Condensor" that is is not required in 1966 since the radio interference suppressor condensor was built into the Alternator itself in 1966. Other than that 1 difference - it is my understanding that the alternator harness is to be the same for both 1965 and 1966