I have a 66 stang with a 289. When I start it everything is fine, after about 20 sec, any light inside the car or outside the car will pulsate. Meaning if the car is running and I open a door the courtesy light will pulsate. the light on the radio will do the same, as is will the headlights and taillights. I have tried 2 different voltage regulators and no difference. I checked the alternator with a volt meter and it stays at 15 volts, no fluctuation. Also the ammeter guage needle does not pulsate.  Any ideas would be great  

Hi stevet - does the pulsing increase in speed as your revs increase? Have u checked all your major grounds in the engine bay? I would think that if all the lights do it then it seems it has something to do with the main feed to your ignition. Will the courtesy lights do it if you open the doors when the cars not running?  

The pulsating does not seem to speed up as the car revs up. Also the courtesy  lights do not blink as long as the car is not running. I did notice that if I drive the car a little bit it will go away until you turn on the blinker or hit the brake or do somthing that pulls current through the elecrical.  

hay stevet - There are surely a few electrical gurus on here - The only things I can think of are maybe there is a short in the ignition, light switch, or dash harness. Use a meter and follow/test the power through your system starting before your voltage regulator and see if there is a location that you start picking up a pulsating voltage as it seams that at some point your hardware will be interfering with the flow of voltage. Best of luck!