I'm sorry for your loss.
Can you post some photos of the whole brooder?
What's the temp under the lamp and on the cooler side of the lamp?
How big is the brooder?
You switched feed recently - what were you using and what did you switch to?
Are you adding anything to the water?
Some photos of the chicks and how they look along with their poop without the red light would be good too.
If you think it's Wry Neck, then giving the chick 2-3 drops of Poultry Nutri-Drench orally twice a day may help. If you have problems with aspiration. Let the chick stand up on a surface while holding it (so you aren't pressing the crop). Take a qtip and dip in your PND, then press it against the beak so the liquid seeps in the beak a little at a time. Let the chick swallow and go slow.