I don't know what that light is, but I can take a stab at it from stuff i've seen... Your charging voltage dropped below a certain thresh hold. I would pull the back cover off the alternator. This will expose the slip rings. inspect the brushes and the brass ring they ride on. The alternator (65 amp or whatever is stock) on my jeep chewed up those slip rings and brushes from all the dirt/sand that kept getting thrown on it. I was charging at a measly 13v with the lights on and engine at 2000 rpm.

91 YJ
2 Seater Sand Rail
Handfull of other fun toys...
And a brand new, spit shined, B.S.
Oh, and a job to boot.