Voltage Regulator
Have you checked the voltage regulator attached to the side of the distributer? RN sells a relocation kit which moves the regulator towards the coil in a more "cool" and secure location.
There is a way to determine whether or not this has failed by checking resistance and voltage to this part. I seem to recall an article on
http://www.rangerovers.net
that should give you all of the details.
Good luck.
1990 RRC, 3.9L, AUTO "Willow Pond" (Sold)
1996 D1, 4.0L, AUTO "Lucas"
1999 RR, 4.0L, AUTO "Belle" (Sold)