If you have RAVE it's pretty clear in the circuit diagram where the stereo's ground is (pointed with red) so go into the Electrical library - Connector views, scroll untill 0361, click on it and you'll see the pic of the ground point it's close to the the driver air bag's connector(there are cases like this one when the location is not well described hence i erased it).... that's how you can find any ground or other connections
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.