Most likely a sensor problem as they are what triggers the anti-lock/pulsing that you describe - most likely a front sensor. When they don't supply a sufficiently strong signal to the ABS ECU it believes the wheel's locking and activates the anti-lock. Could be a poor connection on the co-axial plugs (think they're mounted on the inner edge of the chassis rails), or a duff sensor, or even the cable shroud may have perished allowing one (or both) cables to short somewhere.