Hello, all. In my futile effort to be as stubborn as possible .. perhaps because I also own a Nash Airflyte, I decided to rebuild my own alternator instead of trying another reman, which will likely fail in short order. So I pieced together a bunch of NOS Ford parts from an old local dealer. The truck is a base model 1985 F150 with the I6, and the numbers on the alternator are X40a-xxx. I know they offered a 60a as an option. I have another 40 on the shelf from the same truck, however I also have a, I'm assuming, 75a that I removed from a 1981 Mustang Ghia. It is a small body 1g with X75a-xxx numbers stamped into it. The clocking is the same. The case vents look slightly different, and one of the terminals was not used on the Mustang, though I'm pretty sure it was the one for the electric choke on my '85. I have picked up an HD regulator to go along with it.

Anyway, to cut a long tangent short. Would it be worthwhile to try this 75a, or should I just stick with the old 40a?
The F150 alt is on the left, the Mustang on the right. The rectifier says Made in China so I doubt it was the original to the car anyway.

 

I would try it. The one terminal that was not used was the STA correct? That terminal would not be used with a car or truck that has gauge package in the dash, and has no electric choke like you said. And also the "I" terminal on the regulator would not have been used either.

If you have a GEN light in the dash, then the STA terminal on the alternator would be hooked to the "S" terminal on the regulaor. And the "I" terminal would be used on the regulator.