I recently (2 months ago) changed the battery and the regulator on my 420 to fix a charging problem. Now, when I'm idling, I see the battery light go on. Once I pick up speed, it goes away (around 1500 rpm). Now, this is where I can't figure it out; When I put a multimeter on the battery posts with the engine running, I get 11.91 vdc no matter what engine speed I have the car at. at idle - 11.91v, at 1500 rpm - 11.91v, at 2500 rpm - 11.91v. Could I have another failed regulator or is there something I'm missing here???