Positive ground system or Negative ground system on the P38 02 RR 4.6?
 

NEGATIVE GROUND.
I know the old MG's have/had a positive ground but England finally lined up with the rest of the world on this.

The easiest way to see for yourself is to look at the battery and the battery cables. Follow the black wire from the battery to where it is bolted to the chassis which I think is behind the battery box.

i never knew that anywhere did any of that ass backwards... i guess you learn something new everyday

good to know :)

There really wasn't a standard until the '60's, though most US manufacturers standardized on negative ground in the 50's. Other manufacturers in the rest of the world, most notably the British, kept positive ground until the mid-60's.

You can't always rely on the color of the cable, particularly if someone has replaced the cable.
All batteries are marked with a '+' and '-' next to the respective posts. On top post batteries the positive post is larger than the negative post.
For some reason side post batteries have the same size terminals so you have to rely on the markings.

If the car is newer than a '75 it's definitely a negative ground.