Earth problems in late model Patrols

Hi everyone,I am a Patrol man, and have just bought my second Coil Cab after owning a GQ 94 Coil Cab 4.2 Diesel and doing over 100000 k's without so much as touching the donk.I now own a 99 ST Coil Cab 4.2 turbo diesel and love it just as much, but i am a little dissapointed in the way nissan have set up the earthing of the Electrical system in these new ones.The negative terminal on the battery was earthed to a painted peice of thin metal off the intake manifold and the secondary earth cable went to the bottom of the battery box which is part of the Tin work Body which should give an alright Earth.When introducing any new equipment to the vehicle i.e- After market Driving lights UHF Radio or any other accessory which requires to be earthed the Electrical system depending on the Draw it needs will play up causing any weak earth to react, in this case the Sub Tank Warning light coming on and delaying fuel transfer and staying on untill battery disconetion to reset.I have since ran a better earth terminal to the engine block and UHF radio direct to Battery,touch wood it seems to have worked.I am also wondering does anyone know if the engine water [cooling system] due to bad earth have a positive current runing in it that could corrode components.
Any feedback would be great..
Apart from that the Patrols are a pleasure to own and drive.