After replacing a couple of batteries I decided to check for a current drain and sure enough I have a 2.5A drain on the battery without the ignition on.  I tried disconnecting the shunt and no drain.  I then disconnected the fusible links one at a time and no drain with either disconnected.  I'm looking for next steps so I don't miss anything along the way.

With the fusible links in

1. Disconnect the voltage regulator and measure current.
2. If you still see the drain, disconnect the alternator and re-measure.

I am thinking that pulling either fusible link breaks the connection between the battery and alternator.

Does it have the original voltage regulator?

The voltage regulator is new.  I disconnected it and the current draw dropped to around .4A.  I then disconnected the alternator with the voltage regulator connected and the current draw was still around 3A.  Not sure if it helps but when I first connect the meter the current draw starts around 6A and then gradually settles down to around 3A but it's not steady.

Well, new does not always mean good anymore. If you're using a clamp ammeter, can you measure the draw at each of the wires on the VR?

Also, open up the VR to see if it's mechanical or solid state. If it's mechanical, it may be adjustable.

There was somebody recently (maybe Dolfinz?, who knows) who had a NOS VR, if I recall right, that did not work.  They opened it up and found that one of the set of contacts was stuck shut (I think).  Cleaned it up and it started working.

I can't measure the wires at the VR as I'm using a multimeter and don't have a DC clamp ammeter.  The VR is mechanical and pictures are attached.  I didn't see any type of adjustment.  Not sure why we are focusing on the VR can you elaborate?

@SteveJ

It isn't adjustable. That's not uncommon for aftermarket VRs. If the VR is malfunctioning, the battery sense wire (white in the engine harness) could be feeding the field wire (white/black) that goes to the alternator. On an aftermarket 260Z VR that I have handy, the white/black is connected to a wire wound resistor. If it has voltage all of the time, that could be a current draw.

Plug the VR back in. (Listen for a click in the VR, too.) Unplug the two wire connector from the back of the alternator, and check for voltage to ground on the white/black wire on that connector.

Just for learning, I pointed out the contact points.  That lever in the middle bounces back and forth between them.

So, with the battery connected, the white wire from the alternator disconnected and the VR plugged in I have 12vdc on the white/black at the alternator.  Also, there was no click when I connected the VR with the battery connected.  Next?

I’ve been working on a 2/72 and the owner wanted to keep it original . I was getting a battery drain . The VR looked new. When I plugged it in it would click and cause a drain . Ordered another one and it did the same thing . So now I think it’s the alternator. Took it to an alternator shop and he said it was fine . He also said he had an issue finding a good VR - period . He could a box of them and they would all test bad .

I got rid of the VR