1 be sure that whatever the voltage regulator is mounted on is grounded properly. 2. check the inside of the 12 volt wire from the alternator for corrosion/ electrolysis powder. Use a razor knife and gently slice open the covering of the wire and be sure all the copper is bright clean and pure, no powder. 3. Have the alternator tested, "The alternator actually creates AC voltage. The rectifier inside it then converts the AC voltage into DC." If the alternator, does goes defect and sends AC volts out,,this is bad and may be a issue. 4. Are you overdrawing too many Amps and need a better larger alternator to keep up? 5. Also test all battery cables for internal corrosion, using the razor knife surgery process. Cables can look beautiful on the outside and the covering perfect, and when you open them its OMG look at the krud dust. I recently had a friend with a 65 Mustang 289, hard starting, put in new starter, new battery, new alternator, new solenoid, new regulator, everything but cables because they "looked good". After weeks of frustration he finally conceded to do the razor surgery and while we were on the phone ,,, all I heard was #fu#2*& , look t the freakin corrosion... Replaced both positive cables to starter from battery, and Zoom, car starts every time like lightning even when hot and in 98 degree summer weather, instantly! I have seen corrosion issues in cars, boats, bulldozers, cranes , etc,, and in 12, 24, & 48 volt systems with multiple batteries which all looked good till the surgery ! Also recommend a sealer coating and battery post felt corrosion inhibitors. Find soon, voltage issues can damage and melt harnesses and ignition parts and may cause a fire ! I had a cousin with a 65 Galaxie 390 4 speed 2dr. bucket seats he bought new in New Orleans in 1965! Engine was blue.