This afternoon, we took the truck for a drive. The alternator was intermittent. But the second try to start it worked fine. So we took a 25 mile drive.

Since this alternator has a relay between it and the 12v battery, and the ecm for the truck controlling the ground connection, then a test could be devised that would duplicate either end. For the relay, it could be pulled from it’s socket and a jumper placed across the output terminals. Then I could vary the ecm by just disconnecting it and using some value of resistor to control the current to the field. I’m fairly sure the ecm might be using pwm for controlling how grounded that side of the field gets. It’s works like an electric motor controller. In this testing maybe I will be able to better understand how to devise a stress test for the ecm signal that is controlling the field of the alternator. Maybe a simple resistor to ground with current measurement. Since the field current should be around a few amps worst case, this test holds some merit.