trying to update my Zumo 660, I get a message that there is not enough room in internal memory to download the map updates

Then you'll need a sd card

I have a 32gig SD card installed

Is it formatted FAT32? Does it show in Windows Explorer? 

If you can't get Express to work on your device then as yours is an older device you could install the map to your PC then use BaseCamp to install the map to the SD card.

You'll see that worked here forums.garmin.com/.../1501327

Yes, it's formatted FAT32 and shows in windows explorer.  Will not load to computer as well. 

Sorry but why isn't it loading to your PC? If it's not it's likely that the original issue was not enough free space on your PC. You need up to around 20Gb free, what free space do you have?

If "SUSSAMB" is correct, or you just want to do housecleaning of the PC, this may be of help and potentially can free up quite a bit of space on your PC..

In the folder C:\ProgramData\Garmin\CoreService\Downloads\Map are numerous folders named Map_Map.NA2021.20 or similar. Each folder may represent an old and unneeded map which can be deleted.  Each will be about 6+ GB.

 In the folder C:\ProgramData\Garmin\CoreService\Downloads\Application there are folders named Application_Application.express-windows 7.1.4.0 or something similar. Each of those folders are 112 MB.  Again, those that are old can be deleted.  I personally keep the last one and delete all the others.

In the folder C:\ProgramData\Garmin\CoreService\Downloads\Firmware there are folders named Firmware_Firmware.006-B19948.00.8.80 or something similar. Each of these folders is about 83 MB. I had 40 of these folders, for a total of 3.3 GB!

I have 1.63 TB free, so space is not a problem

Well he says Express won't even install the map to his PC ... otherwise he could follow both my instructions or the one you linked to, which is the same as mine but using MapInstall directly rather than via BaseCamp