BMW Repair: ABS Dashboard light, tire locks, bicycle gear

Question
Hello, I own a right hand drive 1988 325i Touring. I realised that the ABS light wasn't coming on so took the dash apart and found it wasn't connected. Now it's connected it wont go off! I've been told it could be a sensor on a wheel.Someone also told me it could be a relay problem, but I cant find the relay. The only place where my relays are is under the bonnet with the fuses. I changed a few fuses but it still remains on.
If you have come across a similar problem I would be greatful of your help.
Thank you.  

Answer
Hillsey,
 The ABS light can be triggered by a few things.  You have a ring with "teeth" (resembling a bicycle gear) on the inside of your hubs (where the wheel mounts).  This is called a Tone ring.  There is a sensor that measures how fast those teeth are spinning, and sends this measurement to the ABS computer/Module.  If any wheel is spinning faster than another then the ABS will activate.  So if you panic-brake and one tire locks up, the ABS computer will recognize that 3 wheels are spinning and one is not, and it will activate the ABS to prevent lock-up, and loss of control.

  Now you know how the system works, you can try to find why your's is acting up.  First off, make sure you are running the same size tires on all 4 wheels, that can throw the wheel speed off between the front and rear.  Then I would check the sensors on the wheels.
 Look on the inside of the dust sheild, and you will see the sensor.  It's about 1" or 25mm diameter, and has a black wire coming out of it.  The sensor has a ear/bracket that an allen-head bolt secures.  If this sensor is not fully inserted it will give false readings.  Make sure the sensor is seated ALL THE WAY into the back of the hub.  IF the sensor is seated, and the tone ring is clean and free of debris.. then the sensor is likely bad.  You should be able to find new and used sensors anywhere, so as a last resort I would recommend replacing the sensors.

 Hope this helps,
 Good luck
  Josh