There doesn't seem to be any pattern to it coming on. The only way to turn it off is to kill the engine, and restart it. Brakes seem to work alright when the light is on. How do I test it to see what is causing this light to come on?
Without an ABS capable scan tool you would be guessing. Since the problem is intermittent a scan tool is really required since you need to retrieve any stored codes. It could be a sensor, a wiring issue or a wheel bearing allowing enough play to occasionally miss the timing ring.