If you open up the file in a text editor, you’ll see all the Google Earth XML tags. Ignore all the stuff at the top and find the section at the end. If you look at all your KML files in order, you’ll notice that the last coordinate for one file os the same as the first coordinate for the next file.

Copy everything between the tags from the second file (but not the tags themselves) and paste it after all the coordinates in the first file, deleting the duplicate tags I mentioned above.

Open your third file and repeat the process.

Ignore all the other XML tags in the file. When you upload them to GC.com, they are all ignored except for the name of the route, but you can change that after the upload.

i knew i once saw that answer. just had to delve deeply in the old help questions