ABS light intermittently on and rough tickover

[binjam]

W124 1991 300D auto 206,000 miles :
Abs light comes on and stays on run it for 10 -15 miles goes out,stop it and same again.when its ticking over engine labours and shakes the car to bits but when lights out its fine

Heard and read about low voltage's will cause light to come on,so when its runnig for 10 miles or so battery is full charged and all ok?? battery is less than 12 months old and charges at 13.7v.is it possible to just change brushs on this type of alternator or is it service ex unit.

wheel sensors...how common are they to failure
tyre pressure's and wear .if they are causing the problem fault it would be there constantly.. so i cant see that being the problem.

wet weather.. water on sensors/cranked sensor.noticed problen has been more or less there since rain

can anyone explain the roughness in engine while light is on

thanks
Rob