My RrABS and Brake lights have been lit for ummm.......say 3yrs now
That gosh darn RrABS sensor on mine is located on top of the rear axle, and I can't help it

everytime I go down a dirt road (a LOT) for some odd reason I just have a habit of making sure a rock hits that stupid sensor

and wipes it out.
I've replaced that idiotic located sensor 5 times in 9yrs, I'm NOT replacing it again
Those lights can just stay on
But, yes, since your's are going on and off, I'll give you 2 guesses but you're only gonna need one
Hopefully the belt's just slipping. I've got my fingers crossed for you.