I went through maybe three of them.
Here's the story.
MP did not originally sell them as 'race only'
If you look in an older DC/MP tech bulletin (including in the 'Speed Secrets' edition of the Engine book) that's the regulator they recommend when converting to an ECU with a pre-70 car.
They started saying its 'race only' around 1990 when questioned why they would fail. But if you ever dealt with MP at that time you would know that no one there had a clue anymore. The people who had done all the work and had the knowledge were gone.
Here's what I think really happened.
Someone in the program found or knew that the VR for Studabakers mounted the same way as the Chryslers. And they knew or found out these were available in with solid state internals. So they bought a bunch from the manufacturer, painted them blue and put a p-part number on them.
This worked great and eliminated any concerns about switching noise from the points.
I *think* the problem came along when these regulators were used with alternators that draw higher field currents.
You can buy what looks to be the same regulator from NAPA and Standard, except its not painted.
In my experience failures seem to occur when used with squareback alternators, particularly revised squareback alternators.
That's not scientific or statistical, just my observations.
I contacted Standard's tech line, and the guy couldn't find any specs for it. All he could dig up was a dimension drawing. But considering these were intended as replacments for Studebakers, there's no reason it would have to handle field currents of 4 to 7 amps. A revised squareback can draw 5 amps or more if I recall correctly. So can a VR128 or MP regulator survive that long term? I don't know.
What 67Dart273 mentioned about voltage drop will surely make the situation worse. Why? Because it will make the regualtor think the voltage is low and spend more time letting full current through.
