First, are you sure you got the right wiring harness? There are different harnesses for MY 2003-04, 2005-06 (p/n 08L91-SCV-102), and 2007-11.

Then, make sure all the connections are as specified in the installation instructions. And of course check both fuses.

 

And there're always the easiest things to look at first, like it's the trailer or the connector on the trailer is sloppy or corroded on one pin. If the trailer has LED lights and no ground connected (common) then you can end up with all sorts of weird problems depending on how the Honda's converter works. Get a cheap $3 connecter plug tester first and see if it's your vehicle or the trailer.

 

Thanks for the ideas. I finally had time tonight to share the problem and it appears I need a new "trailer unit", as it is named in the Honda OEM instructions. Working from the 4-pin connector at the hitch, all of the way forward to the connection with the vehicle harness, I found all of the connections in good order, as was the fuse. I unplugged the 12-pin, vehicle harness connector from the trailer unit and tested all of its leads. This was the last place I had parking light power prior to the OEM harness.

I will post a follow-up as time permits.
Andy

 

There was a recall on the 05' Harness (wired at the plug wrong), wonder if that was ever done?