Since I posted last, I found out that the alternator that I bought was defective - and I got another one from the store that seemed to work fine... until yesterday.
I have driven the truck for about 50 miles with the new(rebuilt) alternator and everything seemed fine until yesterday when I noticed that the starter was turning the engine really slowly when I started it up to head home. When I got home (5 miles at the most) I turned the truck off and tried to start it up again - and it didn't have enough power to turn run the starter.
I'm taking the alternator and voltage regulator off this afternoon, and having the store check them. Hopefully one of the two will not work and I will know what the problem is. If they both are fine - is there anything else that could be causing the problem? I checked the battery out a few days ago and it's fine (and about a month old now).
Getting a bad alternator from the store, and then getting one that didn't last very long seems strange to me... Is this normal or just bad luck? If the alternator isn't any good I'm probobly going to buy a new one, instead of just trading it in (at no cost) for another rebuilt one. Does this sound like a good idea th anyone else?
By the way, the truck is a '70 F-100 with a 302 V8.
Thanks in advance-
Brandon

 

There is a fusible link at the solenoid that could be bad. The link is mated to the wire that goes to the back of the alt. on the post marked "batt". Use a test light hooked to ground,touching the "batt" post on the alt. If the light lights up, you can rule out the fusible link.Also check the other wires that run from the alt. to the regulator for continuity. Also, the regulator has a wire marked "I" on its pigtail that should get " hot" whenever you turn the key on. If you suspect the pigtail, a new one is available at a parts store,just splice it into the existing wires. Don't be discouraged by getting bad alternators, I used to sell 'em all the time.
Phillip