Gotcha. When you click ‘edit controls’, you are defining custom controls. They are not “inputs”, so to speak. Nothing in front of the custom unit will flow into them. You can set up a signal on those controls’ sub chains, and those chains can use one of the physical inputs as it source (or they can use a global chain, or have their own internal chain).
The linear control is especially good for that. Remember to set the gain on the linear control’s sub chain to 1.0 (or some value other than 0) or it won’t work, and it’s value will always be zero while you scratch your head wondering why. Rookie mistake that I continue to make from time to time.
So on to the second part of your question:
Which of the manual grains unit’s controls are you trying to assign to one of the ‘locals’? If you are trying to process a live input signal, the manual grains does not do that. It only works on sample files. However, you can pull it off by assigning it the same buffer file as a sample recorder that is recording the live input. You could put the looper right in front of the manual grains. Manual grains will block the output of the sample recorder. Then just set them up to point to the same (short) buffer file.