There are a few things that can cause this 1........Regulator, but not always, probably not "usually." 2.........Bad connections at the regulator connector. Pull it off/ on several times to scrub the connections clean, and to "feel" for tightness. Visually inspect them with a light for corrosion 3..........Regulator to battery ground. Remove regulator, clean regulator and firewall, and seriously consider upgrading the grounding. You can run a no10 from one regulator bolt to the engine or battery, or I like to run a no4 starter cable (ring to ring) from a master cyl. bolt to the rear of the engine head 4...........Voltage drop between battery and regulator IGN terminal. Several ways to check this A..........Measure voltage drop directly. Put your meter on the blue alternator field wire (still connected to alternator) adn the other lead on battery positive. With key in "run" you are hoping for a very low reading, no more than .3V (three tenths of one volt.) B...........Measure voltage from alternator blue field wire to ground, with key in run, and subtract this reading from battery voltage. Again, no more than .3V in the two readings. C..........You can do this with engine running. Compare voltage at battery and at alternator blue field with engine running at fast idle, all accessories off. No more than .3---.5V difference More voltage drop indicates problems in the path from battery to regulator. Most probable is bulkhead connector, ignition switch connector, or the switch. If improving the ground or the following checks are OK, replace the regulator
