Diagnosing an LED brake light

Hello good folks,

My left brake light is out on my 2004 Prius. I would rather not replace the entire assembly since the tail light and turn signal bulbs function, just the LED array for the brake light.
Before I start tearing things apart or spend tons of money, what's the best way to find the culprit?
The right side LED array works - do you all know if the wiring harnesses are the same each side? Maybe I can test the LEDs by swapping? Or is there a better place to start with this?

I gotta get this fixed before my next inspection comes due here in VA.

Thanks in advance!
-Mitch