Brightness stuck on maximum setting?

Apple iPad 3G 64GB (1st gen)

I replaced the metal casing on my iPad, which seemed to go well, but then I realized the brightness was stuck at max and can't be changed. Altering the brightness level in settings has no effect, whether or not auto-brightness is turned on. Everything else works fine. Please help me, what could be causing this issue and how to fix it? Thanks!

P.S. The brightness isn't just stuck at software max, it seems to be the maximum output supported by the hardware, slightly brighter than any brightness that can be set through the settings menu.

I tried reseating all the cables including the ambient light sensor. I even bought a replacement ambient light sensor, that didn't help. The issue is the same whether or not auto-brightness is enabled, so I doubt the issue is related to the ambient light sensor.

I figure backlight limiting is tied to some kind of op-amp or an electronically-controlled variable resistor, I would expect if that component were damaged that the backlight would be always-off or always very dim. Give that I would think rather the issue may be related to a short, though I haven't seen one.

I could try replacing one of the other cables like the Display data cable, but I handled the cables well so I wouldn't expect them to be damaged. I could do a continuity test to verify the connection between each matching pin end.

To make it clear none of your suggestions worked (from your first response).