The S2 ABS is not electrical its mechanical if I remember right. The ABS light comes on when the handbrake is engaged & goes out when released. Its more to notify the driver that ABS is fitted not to warn if its not working as the Cossie system does.

As said above get the rest of the ABS removed & then it'll pass. Its because at the moment you have neither a car with ABS or one without. Can't blame the MOT station for that. The car has to be road worthy.