GREAT idea, Jim!
One drawback with the 1-wire is, if the engine starts but never revs, the alternator will NOT charge because there is no 'sense' wire to show the key is turned on.
If left for any time with the headlights or heater on, the battery will drop to 11-volts rapidly. Your new LED indicates, the alternator is not charging (and the engine needs to be rev'ed above 1,500-rpm to get it going.
If an engine throws a belt, this LED might 'flag' the driver before any damage is done.
Of course, the simple solution is to install a 3-wire alt, that way the GEN light will work the way you would expect.
A zener diode with a relay will indicate when the battery voltage drops below your preset.
Last edited by simplyconnected : 05-29-2011 at 11:02 PM.