Don't despair, Iain 
The service manual is on site and it shows the connections (look at file "Service manual 6621-6625" under Beolab Penta, which doesn't contain much else to clutter). Unfortunately, the colours don't seem to quite agree with what you have at hand. The big bunch of orange wires apparently all belong to the midranges - they are connected in two series connected pairs, and so four of those ends are probably just two short loops behind the speaker panel (can't see why they would be wired down to the crossover, only to return without actually connecting to anything there).
For the others, I guess it would be safest to look where they go in the crossover. You'll need to remove the amplifier unit to get at them - I've never worked on active Pentas, but as I understand the only difference is that the five bolts through the bottom are longer as they penetrate the amp as well instead of just the bottom plate!
Some creative work with an ohmmeter might save you from that, but it will be easier to make mistakes...
Plus, there are some images in this thread which might help you.