I am not familiar with your specific cart so maybe someone else will chime in also, but for most carts they seem to be readily available per Google.
Here's one that appears to be for your cart or similar.
http://www.gobookee.net/cushman-gc400-parts-manual/
EDIT: Actually that looks like a parts manual, are you looking for a service manual?
Try this link
https://www.google.com/#q=GC400+manual
1st result on this page.