I have a similar problem with my 68 LeBaron. Now, my problem is not that the lights go off, just that the voltage appears to suddenly change. The "problem" appeared when I replaced the (failed) solid state voltage regulator with a standard one that was sitting on the trunk of my sedan for years (probably the original in the sedan). Dick B. had told me that this behavior is normal of the old regulators, since they have only 3 or 4 charging settings as opposed to infinite charging settings of the modern regulators. It has been like that for over 6 months now, no charging problems. I think though that I have a 35 amp alternator (original was 67 amps), and if I run AC too long at low speeds, the battery seems to lose charge faster that can be recharged (so I have to turn off the AC a bit). I doubt that its the regulator fault though. D^2