2004 Ford Ranger Brake light/ABS light...

My battery light, brake light, and ABS light are coming on. The battery light comes on first, and then in about two seconds the ABS and brake light come on. All three lights stay on for about 15 seconds, and then the battery light goes off, and two seconds later the ABS light and brake light go off. The truck seems to be running and braking fine. This happens when I am driving, but not necessarily when braking. It started doing this about three days ago, and it seems to be random.