Just bought a Auto gauge Air /Fuel meter, however bit confused, says on the back 12V negative ground vehicles only, does this mean anything to anyone as I thought the battery was 12V +

Cheers

It just means that the negative side of the battery goes to the body shell of the car.

Positive ground vehicles are old school, really old school so nothing to worry about.

Coo , that will explain why I could not get it to work correctly as I just wired it up to my 12V charger to see it working, will wire it to car tomorrow.