ABS warning light on dash
 

I recently had my 91' 300SE serviced, they changed the front lower ball joints & now I noticed that when I start the car, the light comes on & go off normally, but when I drive off, the light comes on again & stays on, it only does this in forward, I understand that this is normal when the road is slippery, but I assure you that the road is dry, could this be a damaged wheel sensor? Please advise.
Thanks,
Dino.

Thanks for the tip.
Dino.