You should be able to push a spawner in a minecart using any redstone source, not only a redstone block above the piston. This was tricky to detect before, but it sounds very doable by spawning a TNT sulfur cube inside the piston and seeing if the fuse goes off.
You should be able to push a spawner in a minecart using any redstone source, not only a redstone block above the piston. This was tricky to detect before, but it sounds very doable by spawning a TNT sulfur cube inside the piston and seeing if the fuse goes off.