I've got a '57 F-100 with 5.0 L 302 in it. It's making a screeching noise and the voltage regulator only shows charging at +10.....need a new one or rebuild ?
Remove the belt and spin things, the noisy one will show up. If it is the alternator, take it apart and replace the bearing. Many Ford and Delco alternators from the 70's to the 90's take the same front bearing, as do many idlers on newer vehicles.
If it's not the bearing, I used to rebuild alternators/generators a long time ago, and I remember that a bad diode in the alternator can make a strange electrical noise.
I had an alternator on the family car that had a high pitched squeal after starting the car, I assume when the charge rate was high. Eventually the alternator went out and the new one didn't squeal.
