Thanks, TheOne, good ideas, will give it a go.
I first thought, well this should be pretty easy, 3 pins, two voltages, one should be ground, so the rest easy. Unfortunately.. none of the pins really show low impedance to the shields or grounds on the rest of the laptop, and weird combinations of capacitor charge up between each other. Only one pin shows what seems to be a diode in series with the outer shield on the power jack.
If all else fails..it may be time to get out the ice-cube tray and the JIS screwdrivers!