W500 Backlight Issues

[seahuston]

Hi All,
Looking for some help here as I am running out of options and need to get my laptop working.
ISSUE:
Backlight on my W500 does not work. If I look closesly, I can see the thinkpad text when I start up the laptop so the display appears to be working.
SYMPTOMS/DEVELOPMENT:
The issues started that if I tapped or jiggled the screen it would blink out black. It eventually became worse and then finally just never would light up. External monitor still works.
CURRENT PROGRESS:
Replaced backlight: Did very little testing and thought the backlight was the issue. I replaced the backlight and the issue was not resolved. I know the backlight was replaced properly because I can plug it into my T61 and the light turns on.
Replaced Inverter: Next step down the rabbit hole. I ordered a new inverter and replaced the old one. Still, no dice. I didn't test this new inverter but the LED lights on it work.
Replaced Display Cable: This seemed logical given the fact that tapping the screen caused the issue at first. Still, no dice. I just tried this step and didn't fully assemble the laptop before turning it on. Thinking that maybe the screen open sensor is located on a chip I didn't put back on yet. Still, the thinkpad startup screen can be seen if I look closely.

NEXT STEPS:
Looking for help here.
I'm thinking that maybe the lid sensor is bad. Is this possible and would that make sense if I can still see the display even with the backlight off.
Fuses? It seems like the initial tapping would indicate that it isn't a fuse issue but maybe it is. Can someone point me in the direction of the fuses to test?
Any other thoughts?

Thank you all so much. I hope this gets resolved.

[Zak]

I'm pretty sure screen blanking on lid close will both turn off the backlight and blank the image. If you run Linux or want to check that using a Linux boot disk, cat /proc/acpi/button/lid/LID/state to see whether the machine thinks the lid is open. There's probably also some way to tell on Windows, but I don't know what it is.