Thanks for all the input. it was helpful.

As you both suggested, the failing solenoid was unrelated to my alt/wiring harness upgrade. The age of the old starter is unknown, but it looked rather weary upon removal. All the wiring checked out, no weirdness could be detected. Alternator runs beautifully; steady consistent voltage at battery. I hope I never have to change a starter again. I had to seek assistance in order to get that top bolt out.

Thanks again,
William