I had a 5000A+3 years ago and I can't say that I remember that output on mine. Have you tried it to see if it is providing discriminator audio? Good test would be to go from it to the line in on your PC, and run something like KG-Tone, go to a NFM VHF and above signal, and see if it displays a CTCSS or DCS tone.
Or....I could be way off and that might not be it at all...