Well first off, is there a cable going to the throttle body?
Second, check the Cruise control fuse
Look under the dash and see if there are any wires attached to the sensors going to the clutch or brake. Or do they look disconnected or broken.
Are all the brake light bulbs good?
Is the brake light on in your dash?
looking at the wiring diagram, you need f/b fuse no. 18 and Horn Relay.
Fuse no 16 looks like it powers the brake wire signal that stops the cruise when you hit the brakes.
Does it light up at all?
Never really looked at a subaru cruise control, but normally they have vacuum running to them. Check for disconnected vacuum lines.