So good news, I figured it out. It seems when I took the light cover off it brings down the rocker switch too. The switch is just a two prongs of coper which inside slide across some contacts to switch between the three modes. It seems that in my haste to remove the cover / switch I bent one of the prongs, widening the gap and as a result causing to to constantly contact the live, always on power even when it was supposed to be on the auto-off setting. Pushing the prongs back closer to each other did the trick. Btw, the LED interior light looks super. rather than the dim glow from the little W5W bulb it has a nice white light covering the dash and centre console. Mystery solved...