Do the simplest things first unplug each speed sensor wire and then plug it back up at all four corners and then go and drive it and see if that fixes the problem with the light, there are two wiring harness plugs at each of the front wheels and one plug at each of the rear wheels, unless you have experience at bleeding the brakes do not do this yourself expecially with abs systems you can really screw it up if not done right, leave that to someone who knows what they're doing, by the way I made my living for 13 and a half years as a Certified mechanic so I know what I'm talking about.