Been wondering - had a similar problem show up last year temporarily. Since then it has only reappeared once.
After driving about 20 miles in the rain, had my ABS/Brake lights come on. I did check the master cylinder, and it was a bit low (not excessively) and I filled it. As I had just begun a trip - and I could see no specific problems I continued and the brake light went out after another 150 miles -- and did not come on again.
Similar thing 6 months later.
My suspicion was, I've got a short down near one of wheels although I haven't been able to check it out. The light doesn't stay on when I can get to it and try to check.
