ABS problem-e28

[cwcullen@xxxxxxxx]

I have an 85 535i with an ABS problem-the ABS light comes on and stays on
upon reaching about 5mph. From various digest posts I surmmarize the
problem is probably with one of the sensors. My questions are: Is that
diagnose correct? Is there any way to test the sensors with a VO meter?
Are the 4 sensors interchangeable? (buy a new one, and replace one by one
until find bad one). Are they expensive? Any advice will be appreciated.
Thanks in advance. Wes Cullen

85 535i
BMWCCA 138721 

------------------------------