Ranger,
I am not an expert, but here are some ideas. I think you might have tried this, but I will mention it anyway. To "prove" the alternator, REMOVE THE DA PLUG from the back, and with the truck running, use a wire to jump battery voltage to the "F" terminal on the alternator.
This will put the alternator into full field charge, and with your meter on the battery, you should see the voltage climb to 14 + volts. Don't do this for an extended period of time.
With the key off, the regulator should show battery voltage on #3. With the key off, #4 should show zero volts and when you turn the key on, it should show your reduced voltage. I think you said 7.5 volts.
The schematic shows "F" on alternator to "F" on regulator. "R" on the alternator to #2 on the regulator. These wires, as was noted above have to have continuity...no breaks! I don't know what values in voltage they will have, but if all wires are intact and you can get the alternator to output by jumping the "F" terminal, it would seem the regulator is your culprit.
I know the "no returns on electrical items" is a drag, but you can see why this is the policy.
If you can eliminate the alternator, you have half the battle won. I don't think adjusting the regulator is an option open for anyone other than a experienced repair person. If all else fails and another alternator is required, a internally regulated one would be a good choice, and it could be integrated into your existing system. Good luck.
Stuart
