My cars not running the digiplex setup, but I think a vacuum hose is connected to the digiplex unit. The unit is fitted to the bracket of the power steering reservoir, and there should be a vacuum hose to it from the intake manifold if there should be one. Most probably under the black elephant trunk like hose, and the fact I have a long bit of hose bunged up with a rivet, suggests my car originally used the digiplex setup.
Give us a shout and i'll take a pic. of my engine bay if it helps?