This may be a wrong assumption on my part but when ever my car is running at over about 800 RPM I can see a slight pulse in the intensity of the map light on the dash. Ever since I noticed this I have been using it as an indication that the voltage regulator is doing its proper regulating thing. Perhaps this is an easy thing to look at on your car to get an idea if the voltage regulator is acting up ?? If mine ever stops pulsing I know the regulator will be the first thing I check. I have never liked the battery gauge on the Series ll type dash as opposed to a true system volt meter and wish Jaguar had not gone to it after 1967.
David Barnes
68 E-Type FHC