could be the brake light switch as it is connected. I have a Peugeot 207cc where the cruise wouldnt engage consistently. Digging around the net the brake light switch was the culprit, new switch and problem solved.
This may be the issue with your cruise esp as you say brake lights arnt working!
RAVE said:The brake switch is set automatically during fitment.
If the setting is disturbed, the switch can be reset by
depressing the brake pedal and pulling the plunger
out of the switch body, until it contacts the pedal.