question Intermittent stop light on Zetor 6441

I have an 05 6441. In the last two days the stop light on the left side of the dash has been coming on. Initially it was only at idle, but now I have to push the throttle up to 11 or 1200 rpm before it goes out. No other lights come on along with this. Fluids are good (levels and quality). I wondered about alternator, but the battery light hasn't come on. Any thoughts or help would be greatly appreciated.

battery light lights up when the voltage is too low. Stop light lights up when alternator isnt charging....

Do you measure over 14 volt at the battery terminals ? then it should be good.

I'm sorry I never thanked you for this input. The problem resolved itself and I never checked back for an answer after that. Sure appreciate all you smart folks' input!