I currently have a similar problem.. except my red "brake" light came on right after I changed front pads and bled the brakes. It was weird. Could it be that 2 types of fluid got mixed and this results in triggering the light? They probably are not mixed, but what if DOT3 mixes with DOT4? I heard it's not too big of a problem, but usually they are not mixed. Could it be that my rear shoes are sticking? I have not changed those yet...