You probably want to put your voltage/current/resistance into a "cluster" first, and then make your output be an array of that cluster.
You probably want to look into something called a "shift register" and put your array of data into that. That will allow you to see the data as it collects during each loop. If you only want to see it all at the end, then at the very least you need to right-click the output terminal on the FOR loop and change "Tunnel mode" to "Indexing".
You probably want to add your data into the array with a "build array" node, the "insert into array" you have there is not doing what you think it is.