Measure voltage in the plug across the black and white/purple wire when ignition is turned on, if you get 12V make somehow ti measure with the pump conncted too and if it drops much we'll speak again... do you have RAVE?
My friends call me Fery
2000 Discovery Td5 ES manual
Hawkeye v.6, Nanocom EVO,
VDM UCANDAS, oscilloscope
if you think my english is peculiar it means you didnt hear my japanese
ALL MY ADVICES ARE BASED ON MY OWN KNOWLEDGE AND MY WAY OF UNDERSTANDING THE DESCRIPTION AND OPERATION OF SYSTEMS... I'M NOT A LAND ROVER TRAINED SPECIALIST JUST AN ADDICTED ENTHUSIAST.