From my .vimrc:
match ErrorMsg '\%>80v.\+'
And a screenshot:
I have tried a minimal vimrc and it still doesn't work in the left splits.
Recent Vim versions have the
'colorcolumn' option. It provides the following
:matchhighlighting for something else.
Define a pattern to highlight in the current window
This is fixed by making the original command into an autocommand:
autocmd WinEnter * match ErrorMsg '\%>80v.\+'