Sounds like what you have is the CX-4720 power feed for the radio mount. It should have 4 clear female sockets so you probably have a pin broken off in one of them. If you follow it back it most likely goes to the starter and could be a good source for 24 volts in the vehicle if you plan on using anything that needs 24 volts.
FTM2 USS Long Beach CG(N)-9
US Navy, 1969-1975
1986 M996A1 HMMWV ambulance w/ Kasel M101A3
1977 M880 Dodge Crew Cab
1966 M274A2 BMY Mule
1965 M151A1 Mutt w/ Stevens M416B1