1993 S4 ABS light

[AUDIJIM at aol.com]

I have an "Anti lock Off" light on, on my instrument cluster. The previous 
owner said it needed a rear ABS sensor. OK, no problem. So I changed them with 
known good sensors from a 1992 S4 that had zero issues. After I lifted the rear 
seat to get at the rear ABS sensor connectors, I found the ABS control module 
unplugged! So I plugged it in and took her for a drive. The light came on 
again. I went digging around in the engine bay and found both of the front ABS 
sensors unplugged. So I plugged them in and took her for another drive. No light 
until I step on the brake. And the brake feels sort of hard until I am almost 
stopped, then I feel the ABS pump go on and the pedal goes down a little 
farther and the Anti lock Off light comes on. I have tried to read the ABS control 
unit with my VAG COM, but it is unable to read it. Is the ABS control module 
able to be read? Just to try it, I removed the cover from the ABS pump in the 
engine bay and swapped the two relays and tried it again. No change. I will 
physically change the front ABS sensors and see what happens. I have two brand 
new sensors in the box if I need it, but I will try my "good spare" ones first. 
I just wish the control module could be read. I think that would send me in 
the right direction if it was getting a fault I could read. Also, the rear diff 
lock switch was stuck. It was rock solid with spilled soft drink or candy of 
whatever the previous owner got in there. I replaced the switch and I can get 
the Anti lock Off light to go on and off with the switch. The rear diff lock 
out indicator light on the center consol now works. After I drive it and go 
through the first stop and the light comes on, if I cycle the rear diff switch, 
the light on the instrument cluster goes off. Maybe I have a problem with the 
rear diff lock out indication switch at the differential?

Any thoughts?

Jim