Voltage @ cruise

I am doing the same thing with the duster I just purchased.
Start it up and you can watch the voltage climb, I seen it as high as 15.8 volts.
The ECM when I bought the car had already had the epoxy on the back running out of it and down the inner finder.
It ran long enough to get it on the trailer and back off before the ignighter in the distributor took a crap.
Changed the voltage regulater and no change.
I bought a one wire alternator but have not have time to install.

My dad had the same problem on this 78 truck about 10 years ago, and it wiped the amp gauge out, which everybody knows kills all the electric to everything.