I have a MK IV golf and for reasons that I won't offend you with (to do with Empeg replacement ), I need to switch a relay from the dash illumination circuit. Because this is on a dimmer, the voltage on this circuit measures between 2v and 12v depending on the dimmer level. I know I could find a full 12v lighting circuit , but it would be a much neater solution if I could work off the illumination circuit at the stereo connection. Can anyone suggest the simplest way of achieving this.