I am not going to be driving the car tomorrow as it needs some time to get looked at. When I bought the car the ammeter worked as it should, not like it did in the video. Then it became intermittent. Now it does it full time. The battery is basically brand new as I bought it to replace the one the car came with. It has never run low or needed a jump and always starts the car fine. I guess I would like to know what would cause the gauge to act like it did in the video? Is it a problem with the gauge, connection on the posts, or something else? All other wiring is intact and not butchered. Car has an original 94k miles on it
Are you comfortable with drawings? If so, the ammeter's movements will make more sense after looking at the diagrams in my link above.
The movement in your video is telling us current is flowing from the alternator toward the battery. Specifically, the flow increases from near zero to 20 amps when we hear the engine rev. That's not intermittent per se, its responding to flow.
To know why, will require some more testing or more info from your observations.
We know some things to start with.
The current only flows when something calls for it.
Alternator potential output increases with rpm.
Something on the battery side of the ammeter was calling for power - maybe the battery, maybe the pertronix if it was attached to that side, maybe a short.
The alternator doesn't have enough power output at idle to satisfy that demand, but as rpm increases, its output increases and the demand is met.
Its worth checking the battery condition because many times the stock alternators could barely provide enough power at idle for the ignition, lights, and wipers or other accessories. Over time, the wires and connections oxidize, and sometimes get loose. This means even less current and voltage to keeps things going at idle, so the battery takes over every time the car is idling. Then when driving, the alternator recharges it. The lower the battery charge is, the more current the ammeter gives it, when it can.
In the above situation, the culprit is low alternator output at idle combined with poor or loose connections.
A similar situation will be if just one of the alternator diodes fails. The alternator still puts out power, but only 2/3 of what it would normally. At idle, this is terrible. If you saw the battery discharging at idle - this may be the problem.
A voltage regulator failure could indirectly cause similar symptoms if the battery was low. If the voltage is high, or goes up with rpm, (another reason to be checking with the voltmeter) the regulator is stuck on full field power. If the battery is low, then once again current will increase with the rpm. But in this case its because the voltage is allowed to climb. Or, I've had this on some of the new solid state ones, where the regular just gets a little flakey.
Another reason for a regulator to full field when it shouldn't is poor connections in its circuit - usually a bad terminal crimp or oxidation at the bulkhead. If the regulator see less the 14.5 ish Volts, its going to let more current through to the alternator's field. The regulator here is just doing its job. If its getting under 14.x volts, it thinks the alternator isn't putting out enough power.
Measure the voltage at the regulator connection.
Last,
if the pertronix is wired to the battery, and if its going flakey and now drawing more current than before, this, plus the poor connection be causing what you see.
And going back to the begining - if there is a short - the insulation missing anywhere and a wire touching a ground its going to draw as much power as the alternator can send it.
edit: I'm thinking this is less likely - assuming your battery is still connected. Because if there is still a short in the charging wiring, the battery will discharge through it - and you would have noticed that immediately!
