RE: getting the source finding button in c-h f help buffers to work

[Drew Adams]

> there was a thread about that here a while ago:
> 
>   <http://lists.gnu.org/archive/html/help-gnu-emacs/2016-
> 02/threads.html#00004>
> 
> The gist is you can set a variable `find-function-C-source-directory'
> to tip Emacs in the right direction.

I think the OP is talking about Lisp source files, not C.
He mentioned byte-compiled files.