You should have it checked at a garage,it could just be moisture/damp in the box as happens on trucks.A lot of people remove the bulbs but this is very dangerous you could end up with no brakes if it sticks in that mode.ABS AS FITTED TO HEAVY TRUCKS HAS CAUSED SEVERAL ACCIDENTS WHICH HAVE BEEN KEPT UNDER WRAPS.Travelling on a rough road surface with abs can lead to your braking distance being increased two or three fold as the suspension bounces.It can be a severe driving hazard to inexperienced drivers.