garmin downloads to sd cards

This is just a guess on my part, but make sure your SD card is formatted FAT32. To check this, put the card in your computer card reader, then in My Computer, right click on it and select Properties. The File Sysem should show as FAT32.

Hmm, according to the owners manual (page EN-38):

http://static.garmincdn.com/pumac/KNAG510_OwnersManual.pdf

the update should instantly be recognized and installed. I wonder if the SD card is bad or the download is corrupt.

I assume you got the download here:

https://buy.garmin.com/shop/store/downloadsUpdates.jsp?produ...

[Or, as alandb suggests, the card needs a format before copying the file and installing it to the Kenwood]

What is the name of the file you placed on the sd card? Did you copy the KNA*.exe file to the sd card or execute the file to unzip the update files to the SD card?

(From Garmin's download page)

Installation Instructions
1.Create a 'garmin' folder on an SD data card (must be at least 16mb space available on the card).
2.Download the appropriate self-extracting archive file onto your hard drive.
3.Run the downloaded executable file.
4.Click on Browse and select the SD card reader in the list, then select the 'garmin' folder.
5.Click Unzip to save the files onto the 'garmin' directory on the SD card.
6.Wait for the message that the update was unzipped successfully and close the updater.
7.Safely remove SD card from PC.
8.Make certain Hideaway Navigation System is off.
9.Insert SD card into Hideaway Navigation System. If there is already a card there, temporarily remove it.
10.Turn on Hideaway Navigation system.
11.Your Hideaway Navigation System will ask if you would like to update software. Answer 'Yes'.
12.The update will begin. Do not power off unit while the update is in progress. When finished you can verify the update by checking the version number in Menu->Settings->About->Software.
13.Remove SD card.

I know my nuvi 660 will not recognize Mao files bigger than 2 gig on my SD card.

as Bear007 stated the downloaded file must be unzipped before installation, and if it is not read, try shutting down the unit and then inserting the SD card and reboot so that it would recognize the card.