Disco 98 Cruise Control / Alarm issue, related?

Hello,

I just bought a Disco 98 a week ago and am trying to get the cruise control working. I get the master switch to light up, but the cruise control doesn't kick in if I press the 'set' button at say 60mph. So I did some digging around, replaced the vacuum pipes that go from the brake pedal into the pump/other thing. Now, the interesting thing.

Under my Dash I have a black box (FCC code is JT3KDT1786-R) with one big connector on one side, and lots of connections (about 4 small and 1 big) on the other side. I assume this is the Theft Alarm System? it has a bunch of dipswitches on the side, about 12, what do they do?. One side of mine is not connected, if I connect it, the car goes into Immobilisation mode and all the lights flash until I close the doors. I've tried opening/closing with the remote, it still works, but it doesn't stop the flashing, nor does it disable the immobiliser. So I unpluged that box again.

Is there a way to get that box working again? and do you think that is what is breaking my cruise control (I notice a lot of the wires are the same).

Thanks

Graham