Your speedometer variable is grey, it should be blue. Do you have the reference set at the “Event Begin Play”? In the big picture, top left corner, there at my “Begin play” where i create my widget, i also made it a variable, which i use down there at the end.
This part i mean:
The center part is where i set the variable for the casting to the widget.
Edit: Ok, turns out, you don´t even need to cast to the widget, if your variable is set correctly. (casting is one thing, i never really understand ^.^)