You don't say what year 850 you have, but bad ABS modules plagued the 96 model year. Sometimes it's wiring crimps to the ABS unit (probably the harness you had repaired in your previous 850). More often, however, they'll replace the module - a pc board or soldering that cracks.

Another source of the problem could be a fouled sensor in one of the front wheels.

A trip to a dealer or indy tech could help you find out whether a tell-tale code is stored in the OBDII system.

In the meantime, turn off the TRACS unit before you start off to avoid annoying brake chatter, and perhaps premature wear in the brake or ABS system.
--
David
98 S70 T5SE // Black, misc mods (mostly lighting), red calipers
92 940GLE // Hella Micro DE foglights