Does your traction control work after you get the message? If it does, it is most likely NOT the ABS pump but a rear wheel sensor like you suspect. That's what the wheel speed sensors are supposed to do. If they sense an imballance in the rear wheel speed, they tell the TC fairy to engage. And the ABS light goes off because our GEN 2 Marks have a TC system that uses a combination of braking, throttle and transmission to work. You are probably getting the "CHECK TRACTION CONTROL" error message when your speed reaches about 15 MPH the first time you drive after an initial start-up, right? You are probably also getting the ABS light on the dash, too. That's just the car's way of saying "check me out, fool! I need more money spent on me today!"
I recently experienced the same problem with my '97 and a friend of mine that works as a service tech at the local FLM stealership told me it was probably a rear wheel sensor. Haven't gotten around to fixing it yet, though. If you don't mind driving without ABS (I actually like not having ABS!) and don't want traction control (I only use it if I'm driving in deep snow, the rest of the time no TC so I can crank 'em off if I want to!!!), disable the traction control before you take off. If you try to disable the TC after you get the error message, it will not clear. You'd have to stop the car, shut it off, restart it and THEN disable the TC. It is an annoyance to me so far, but I'll get to the sensors once the weather gets a little better around here. I'll have my buddy give me a hand and hopefully it won't be too tough of a fix. Seems to me that the wheel sensors are under $50.00 each, but I haven't checked to verify.
Good Luck!