So after having got my '67 D200 up to driving condition recently, I went ahead and moved on to the charging system.

Not long ago I replaced the old, tired alternator with a remanned unit that has worked well. The problem was that sometimes the truck would charge, and sometimes not. When it did, the ammeter in the cab would tend to jump around a bit, but not enough to be a major red flag or anything. I tried to figure out the charge / no charge condition for a while and I ultimately found that if I unhooked the ignition wire going to the voltage regulator from the ignition switch and hooked up a jumper from the battery to that terminal, the truck would charge just fine all the time.

Fast forward to this past December and the ammeter fluctuation seemed to be getting worse. Additionally, I found the truck wasn't charging more often than it was. Now, even if I hooked a jumper wire I wouldn't get anything out of the charging system. For the record, the regulator did appear to be a original unit and was in near pristine condition on the inside and outside. This now full time no charge condition prompted me to go ahead and spring for a new regulator, to which I installed shortly. After firing the engine up, I hooked an analog load tester up to the battery and just used it to monitor voltage instead of relying on the gauge in the cab. It was charging again, but had a rapid voltage fluctuation on the battery going back and forth from 12 to 14 volts as fast as the needle could move between them - the same as it was doing with the old regulator. I then unhooked the wire coming from the ignition switch in the cab and hooked up a wire directly to the battery. Just like that, it was now charging a smooth and steady 14.2 volts as long as I kept the wire attached.

That is where I am today. I don't want to hook the ignition switch back up to my new regulator again in fear of blowing that one too. I've tried doing some research on this, but haven't found any solutions to this kind of issue as everything I have seen just ended up being a bad voltage regulator. I do have a 67-68 service manual on these trucks and for "Excessive Ammeter Fluctuation" it says "High resistance in the field circuit to the alternator or an improperly set voltage regulator" which doesn't prove true in my case since the charging system works perfectly fine when I connect the regulator to the battery directly.

At this point, I'm pretty sure this just boils down to a bad ignition switch, though I can't say for certain.

What are your thoughts on this?

Thanks.