That is the reverse lever switch, but please don't get discouraged.
According to the Honda parts fiche, the gear position switch (35759-MN5-003) is no longer available for 88 to 97 GL 1500s. Looks like reverse won't be a working option on the 1500 eventually unless some after market supplier decides to start making the switch.
The switch is available for the 1998 to 2000 models, but it has a different part number and the books don't show any interchange for earlier models.
Yes, Straightwings has a lot of Wing parts, but not this switch.
I have a parts request in at Western Honda, bu haven't heard from them yet.