Just to add into the discussion on feeding magnet wires, I found that I needed to feed them straight up the tube, from the bottom, and then use a small fabricated pick to pull them out at each signal head. When you try to do a three head signal, even with a common mast for power, pushing wires the other way is difficult.
Here's an old thread:
https://www.therailwire.net/forum/index.php?topic=31256.msg396837#msg396837
