I replaced the ball joints and put it all back together and now my ABS light is on constantly.

What should I look at?

Drove it and the brakes work fine as do the ABS

 

Did you plug the sensor back in on the hub unit? Could the wire or the hub unit have been damaged in the process?

 

Double check the connections and look for any signs of a break in the wires. You can ohm the wires at the connectors. Also, you can check for AC voltage as you spin the wheel.

 

Mine did the same. The eye on the sensor could be dirty. I am going to replace both front ones in the spring. As you know how much pain it is to pull it apart.

 

This makes sense, as everything else was fine

 

Do you have AE, or other way to read ABS codes? If not, the simple wiring checks with a DVOM or analog meter will tell which sensor, or wire, may be at fault. No use in tearing into it until you determine the source of the problem. A weak voltage reading when the wheel is turned would indicate a dirty sensor. Set the DVOM to lowest "AC volts" scale and look for a fluctuating reading up to 2 volts while spinning rapidly. If less than 1, you're getting a weak signal.