Your pretty close. The power goes thru the 161 battery light bulb to excite the regulator ( no Led's ) and the regulator has a ground for that and the light comes on. Then when the alternator starts to turn there is a reverse 12 volts that goes back to the bulb and null's the light to turn off. Think of a slinky toy that is going left and right as the hands move a little. The light does almost the same by turning on and off. As long as there is about 8 volts coming out of the alternator and going back to the light it is off but if the alternator starts failing and not generating enough volts the bulb comes back on. It's like in a state of limbo. John Hervey www.specialtauto.com -----Original Message----- From: dmcnews@xxxxxxxxxxxxxxx [mailto:dmcnews@xxxxxxxxxxxxxxx] On Behalf Of daviddlasvegas Sent: Thursday, August 30, 2007 10:32 PM To: dmcnews@xxxxxxxxxxxxxxx Subject: [DML] How does the Alternator light work??? My curiosity has been peaked with all this electrical system trouble I've been having. I'm wondering if anyone can tell me exactly how the alternator tell tale light works. Here's what I'm thinking: There is a positive wire from the battery that goes to the light. The negative wire from the light goes to the alternator. When you turn the key on, the alternator is not making its own power yet, so the juice goes thru the light and is grounded at the alternator. Thus the curcuit is complete and the light illuminates. Once the alternator is on and making power, it can't act as a negative and the circuit is undone and the light goes off. When the ignition is turned on at first it takes a few seconds for the alternator to start making power, so the light illuminates for a few seconds (while the manual says this is a bulb check it's really just electricity working the way it is suppose to). So how close am I??? To address comments privately to the moderating team, please address: moderators@xxxxxxxxxxx For more info on the list, tech articles, cars for sale see www.dmcnews.com To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews Yahoo! Groups Links To address comments privately to the moderating team, please address: moderators@xxxxxxxxxxx For more info on the list, tech articles, cars for sale see www.dmcnews.com To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/dmcnews/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/dmcnews/join (Yahoo! ID required) <*> To change settings via email: mailto:dmcnews-digest@xxxxxxxxxxxxxxx mailto:dmcnews-fullfeatured@xxxxxxxxxxxxxxx <*> To unsubscribe from this group, send an email to: dmcnews-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/