Adding the word “custom” to a forum search helped me solve the issue.
Coding for a GR3 FTP status check is built in to the include-wxstatus.php file, but I had to add this line to the custom checks space in wxstatus,php to get the check to work:
do_check(langtransstr("GRLevel3 Radar FTP"),$GR3file,60*10+15,'file');
I copied the line above from the GR3 syntax in include-wxstatus.php. The FTP status check is working, so I assume what I’ve done is correct.
Thanks for your help, Vasco. I stumble through this stuff pretty much blindly, but a little help here and there makes a big difference.