2000 vauxhall vectra 2.0 cdx - vectra maf wiring test - melvyn

hi

i want to test the wiring on the plug that goes into mass air flow meter on my vectra there are four wires marked 1 - 4 what i need to know is which wire is live and which is earth

1 brown

2 blue

3 red

4 green and brown

regards

melvyn