Hello!
What did you use for the LED Number? The LEDs are zero-indexed starting at the user controllable LEDs, so to turn on the User1 LED ( the first user controllable LED), you would set the input LED Num to 0. To turn on/off the USER FPGA1 LED, you should add the FPGA target to your project. Then, under Chassis I/O, you can find the USER FPGA LED I/O.
This KnowledgeBase article goes a little bit more into the RT LED VI, and talks about the zero indexing:
Accessing the User LEDs on a cFP or cRIO Controller: https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019OgcSAE&l=en-US
Hope this helps!
R Dahlman
