Lamber Sensor???

[wide_saxo_vtr]

I have just been given a 'Air/Fuel' gauge off a mate and he has no instructions to fit it! I know the basic layout apart from I have to connect a grey wire on the gauge to something called a 'lamber sensor'

Does anyone know where to find this lamber sensor cable?? or has anyone fitted one of these before, if so have you any advice to help out please??

Thanks Fellas!