I can't understand why you are unable to check voltage while cranking, ask somebody to turn on the ignition and measure on the battery cos if it's some short circuit the voltage drops even if the battery was tested... if no voltage drop on the battery measure on maxi fuse MF1 (100A) in the engine bay fusebox and if you have voltage there and nowhere else replace the fusebox
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.