Thanks for all the suggestions. I found the part loose in the
passenger footwell of the car. Someone else probably pulled it loose
before I got there.

I found the Honda Lock Mfg Co's website, but it wasn't much good to me
as it's in Japanese.

I zoomed in closer on one of the pictures I took and got this view of
the label:
http://www.mythic-beasts.com/~cdt22/...part_label.jpg

Anyone know what that means? There appears to be some kind of
connection diagram on it.

Best wishes,

Chris