Help diagnosing ABS OFF?

[Myke456@aol.com]

I am about to begin troubleshooting my ABS OFF problem. 

Details: 87 5kcsTQ, pads and rotors are in good shape, light comes on after
driving 1/2 mile, reset ABS, light on again after 1/2 mile. (diff locks are
OFF). What preceeded this was the ABS OFF light would come on, I'd reset
it-all OK for about a month. Stayed like that a few months, until the
frequencies got closer and closer together, until what I have now. After
following other similar posts, I now plan on checking the wheel sensors. 

My questions:
1) Before I start, should I get a new set of the plastic caps that go on the
ends?
2) Is there a way to check if the sensors are bad?
3) Anyone have any advice on anything else to have on hand?
4) The big one-Would anyone care to give a step-by-step on troubleshooting
the sensors or narrowing down where the problem is?

Thanks all!

  ([____]=====OOOO=====[____])   87 5kcsTQ, 196k miles
 []]]]]]]][Mike Aiello][[[[[[[]     original owner
___\}}}/________________\}}}/_______myke456@aol.com
       Dutchess County, NY