Amp meter does not register

Hello,
There must be a bad or loose connection. I would make sure all the grounds are good do a visual inspection of as many as you can find make sure the one that goes from the engine to the body is good. On a ride that old there maybe more than one. Then if you can get another person to help set them in the car running and watching the gauge then you go through and just start touching and moving the harness and the wires around and see if you can get the gauge to move even just a little. Has any work been done lately, any jump starts?
Let me know,
Tom

Here is a guide to help check the wiring with the alternator wiring diagrams as well:

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (below). Please run this test and get back to us.