ABS on, but not working (diff locks?)

[Myke456@aol.com]

I've stopped my "ABS off" light from turning on (87 5kcsTQ) within 1 mile of
starting off, by having all the sensor caps replaced (3 were cracked). Thanks
to all that responded. However, the system itself isn't working as follows:

1) "ABS off" light illuminates when ignition power is initially turned on,
then shuts off when engine starts, and stays off while driving--as normal.

2) If, while driving, I push the ABS switch, the "ABS off" light illuminates.
Push the ABS switch again, and the "ABS off" light shuts off--as normal.

3) I've done a number of intentional braking tests on ice/slush and have
found the wheels lock up (definitely no ABS action) identically when the "ABS
off" light is illuminated and off.

I've checked the fuse in the ABS controller (left knee relay panel)-OK

Anyone have any ideas on what to check next?

Possibly related:
I tried engaging the diff locks to see if the "ABS off" light functions
normally. When I go to position 1, surprisingly, I get no diff lock indicator
light, hmmmm.( I checked the bulb-its OK) and the "ABS off" light DOES NOT
illuminate. When I go to position 2, just that diff lock light illuminates,
and the "ABS off" light also illuminates--as normal, except for the position
1 light-not on.

Could a problem in the diff lock cause the ABS not to work at all?
Any ideas on how to proceed on the diff lock function?

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