How to use program G7ToWin to retrieve your HWID:

Download the appropriate version for your Win OS (32 or 64 bit) from the below attachments:
[Only registered and activated users can see links. ]
[Only registered and activated users can see links. ]

Click "File", then configure it correctly for USB (some very old units use a COM Port not USB):

G7 To Win Config

g7towinconfig?w=640&h=506 (thanks Alexander for the screen )

Connect device in *[Only registered and activated users can see links. ] after selecting COM Port/ USB and in GPS menu click on Get GPS ID, like this:

[Only registered and activated users can see links. ]

*Older 'region-only' devices without a visible file system are in a perpetual pseudo-preboot so may simply be connected while following any prompts on the device screen.

Or for units with a visible file system look at Garmin folder for GarminDevice.xml in Mass Storage Mode [See "<PartNumber>006-Bxxx-00</PartNumber>" where xxxx is 4 numeral HWID]. If you have a backup, look there.