After 2 years (10-2007 to 10-31-2009), the TRACS/ABS re-started working on our 1997 850.
I was cleaning fallen leaves (pine needles), and jiggled the housing that is at the front of the ABS module. The HOUSING was loose, and on further inspection its plastic pivot was broken, so I lifted it and just wiggled the connection underneath, not even thinking about the fact that it was attached to the brake/ABS module.
The black plastic housing reads "Volvo 914850," and a very small AMP965513. It is above the transmission case, below the master cylinder, and in front of the silver box/black cylinder on he brake module assembly.
The connection is at the end of the 1/2 inch diameter plastic cable housing that runs into the housing--It is the only big electrical connection around.
Anyway, now the ABS, odometer, speedometer, and cruise control work, and the ABS light is out.
I do not know if this is a unique situation, but I hope not, so you can have your ABS/TRACS work.