What is the part # for this?

Bless my soul, that looks like a picture of a rear combination light from an early Gen 2 ... the ones where the brake lights looked black when off, and continued the line of the black lower glass in the hatch.

The cool thing about those is it wasn't done with a tint. That lens is water clear, just as in the two lower sections. And the reflectors are plain silver mirrors. They just happen to be aimed at a black surface below them, so you see black when the LEDs aren't lit.



So, because that section uses LEDs built into the assembly, rather than a replaceable light bulb, if the LEDs really aren't working, there's no official fix other than replacing the assembly. I think some people have taken it apart and done soldery stuff to replace LEDs.

Of course, check all the wiring and connections leading to it, before deciding the combination light is the problem.

 

I'd think for Gen 2 parts, recyclers would be a favorite source for such things these days. You get an OEM part, and cheap. If you're afraid it's old and might fail soon, buy two.