Richie-Van-GTi 81 2 Cars Posted March 20, 2007 does the battery light have a permanent live with a switched earth or a permanent earth with a switch live? Im in middle of finishing my gauge pod and need to know desperatley. Share this post Link to post Share on other sites
jim21070 2 Posted March 20, 2007 IIRC it has +12V on one side and gets an earth to illuminate it through a stopped alternator. As soon as the alternator is spinning an putting out a voltage the lamp effectively sees +12V on both sides of it and it goes out because the potential difference across the bulb is 0. Note that the +12V that comes to the alternator via the lamp is necessary in many cases to provide an "excitation" voltage to kick it off amd make it generate a charge. A non charging alternator is sometimes just simply down to a blown bulb. Some bulbs even have a resistor across them so if it does blow the alternator keeps an excitation voltage. Share this post Link to post Share on other sites
