Hi, Not sure - try checking the wire colours with a wiring diagram to see what they should be for. Maybe for something you don't have fitted as there are redundant connections on mine.
Griff
Purge cycle is with ign on, press accelerator fully 5 times. Engine management light will flash and run the cycle to purge air from the fuel system.
Not a difficult job. How To on UP's site here
http://www.discovery2.co.uk/Injector Seals.html
Griff
Yes there is a none return valve in the fuel filter housing. Rear outer if I remember, but please check. Does it start after doing the purge cycle? If so I suspect its the injector copper washers. Plenty of info if you search.
Griff
You have 2 seals on the injectors. Bottom copper one will allow combustion gas into fuel and cause starting issues, Rubber O ring seal will allow diesel into oil and cause oil level to rise on dip stick.
Griff
Have you tried starting it after dong a purge cycle? If it does then there's air getting into the fuel system and may need the injector washers/copper o rings renewing.
Griff