My main 62 has always been a bit low on charging. The output on the alt usually is just below the mid line on the gauge or 10ish volts at idle. When it would go up to 1500 RPM or so I would hit 13-14 volts. That is normal from what I have seen on them with older alternators. I have had 2 used alternators on it with the same results more or less. The current alternator just crapped out. It happened to crap out right after I set up the dual batts. The dual batt set up is correct and even if I isolate the primary batt it is still a dead alternator. I bought a NAPA reman and installed it. More or less it had low output no matter if both batts were hooked or not. It would not charge at all once I started the truck until I got it above 2500RPM then it would kick in and work but it would not read more than 12V no matter the load or the RPM. I pulled a known good OEM alt off my other 62. On the other truck it read 13.8V at idle and 14.4 at 1500 which is good/normal. Under load it would fluctuate a bit then stabilize back at the proper voltage. I installed it on the other 62 and got almost exactly the same results as with the rebuilt NAPA alt. 10 V or so at idle. Gets up around 12V at 2500 RPM or better. It never will go over 12.5 volts no matter the load. All this is telling me there is an outside issue from the alt. All wireing is new or checked, batt leads are custom and test out perfect. The charge light does not come on ever. Could this cause a low charging condition? I read the diagram and did not see how it could but? If the charge relay is out would that cause the issue? Bascially I have low charging no matter what alt I use? WHat other issues can there be?