I would like to share an improvement I did with my Range Rover P38 ( 1996 model ) and soon will do with my 'new' Patrol 1989 model.
I noticed in the RR that the EARTH wiring made a weird circuit : from battery to engine to a single point at the chassis. With that much electrics going on I thought 'lets see what happens if I make a few 'short-cuts' ... no not + on - ... you get what I mean. So I made a dedicated Earth wire from battery to ignition pack (8 coils in that RR ) , one to the main fuse box under the bonnet and one to the sub-fuse box under the drivers seat. Don't ask how many fuses that RR has ... you'd faint.
The result: improved fuel economy !!! Most likely got a better spark due to better voltage on coils. Improved responsiveness of the climate control ( a common RR problem) , all regulated with motors, brighter lights of all switches etc.
It is not hard to imagine that when a vehicle gets older the resistance in the original Earth wiring increases. The dedicated Earth wiring circumvents that. make sure you make good lugs ( soldered ) and make good contact to the various points.
I'm sure a similar action will improve something in our Patrols.
Good Luck !!
J.