Originally Posted by johnmn

The light probably failed due to water leaking into the light through the old adhesive based seal, corroding the connections. Ask me how I know. You'll want to buy a new gasket seal while you're at it. Would be good to replace the seal on the right side as well.

Here's a youtube do-it-yourself guide:

https://www.youtube.com/watch?v=KGZ3GxH0Fs0