Let me start by saying I know just enough about electronics to be dangerous. I can read a schematic and am good with a soldering iron. I have put together two sequential taillight circuits for my 65 Mustang. The circuits works well when I have them inside my house hooked up to a 12vDC power supply. When I install them in the car however the voltage jumps around so much do to the lights come on and a variation in alternator speed that it is making the sequencing of the lights erratic. I believe the voltage variance is between 8 and 14 volts. The circuit uses less than 0.2A. What I am looking for is a way to keep the 12 volts constant. My first thought was to use a 12V zener diode to limit the power. There are two problems with this, one is I am not sure how to use a zener diode to limit voltage, and two what do I do about the power dropping below 12 vDC. I think I could install a capacitor to help maintain voltage, but I am not sure where to put it or what uf to use. The catch to this is that when the turn signal flasher turns off that is what cuts power to the 556 timing circuit and resets it so the cap cant be to big. HELP!! If you need more info let me know.