2007 honda odyssey antenna wire

2007 Honda Odyssey EX-L no Nav no Rear Entertainment System. Hi, looking for info on the Honda factory antenna - the factory antenna harness has a coax (square connector) and an additional conductor (black wire). I know what the coax does but does anybody know what the other conductor is for? During testing of my install (Kenwood DNX-7100) I connected the antenna (using AI HO-6 adapter cable) leaving the additional conductor unconnected. Reception on AM/FM seemed OK - just not sure what to do with this wire - it has no voltage on it and resistance to ground is in the megohm range. BTW, the HO-6 adapter did not fit the factory connector! The outer metal shield on the coax cable in the HO-6 is a bit too big to fit thru the plastic guide on the factory connector shell. I removed the factory coax from the factory shell and the HO-6 cable does fit, so I'm just planning to slightly enlarge the opening in the factory plastic shell. Trying to make everything plug and play so I can easily reinstall the factory radio at trade in time - so far so good including steering wheel controls (SWI-JACK). May need to make one splice into reverse indicator wire (for backup camera) - anyone know the best place to tap this conductor? TIA

use the Metra 40-HD10 antenna adapter. the black wire in the factory antenna adapter is the antenna amplifier turn on wire.