Amp gauge...jumping!

Thought I would ask if anyone knows why my Amp gauge jumps around.
Only does it while the engine is running.
About every 5 or 6 seconds the needle slams to the left, then comes back to normal.
It is so quick that if you blink you won't see it. But you can hear the click when the
needle hits the side of the gauge.
My car is a 67 Belvedere.

It's shorting if it's jumping to discharge. You'll have to find the problem before it jumps and hangs there. First thing I would check is alt field wires.

more information of what kind of charging system you have...
Need to get out your mult-meter to do some checks...
Must have a fully charged Battery 12.5.. If you are properly charging @ 13.9 TO 14.2. YOU need to look at.. Voltage drop. possible alternator die-ode, loose connection at a positive or field wire...,check the brushes in the alternator, and that the screws that holds the brushes are tight...wiring harness at the bulkhead main splice..Checking all ground & wires in charging circuit. loose connection at amp gauge at dash...or ground at dash...

Instrument Gauge Repair - Tech Articles - Hot Rod Network

Check the studs on he back of the gauge and the wire connections to them to be sure they are tight. I recently found the studs loose on mine. Since I had to go in, I just pulled the wires and bypassed the damned thing.

All good suggestions.
I'll start looking tomorrow.
Thanks.