I know what you're trying to say... but this reads like very dangerous advice and you may want to revise.
Ammeter between a battery's terminal and the car's electrical system.
Also note that you'll probably create sparking when doing this, and if the battery has recently been charging this can be dangerous (hydrogen outgassing).
Yah, that doesn't really make sense for small parasitic loads.
> Ammeter is not safe as general advice as a typical one won’t be anywhere near large enough capacity for working with a car battery
It should be fine with the car not "on", but the general level of danger of doing anything near a car battery requires caution.
If your multimeter has a sub-mV range -- which a decent meter should -- you can measure a voltage drop across the battery ground lead. I've successfully done that to diagnose a battery draw in my car.
It's the same principle as measuring the voltage across a fuse, except it ends up measuring the draw for the whole car, not just one circuit.
No. Not if the meter is in "Ammeter" mode (or is purely an ammeter only). An ammeter presents a very low resistance to the circuit you are attaching it to, low enough that for almost all circuits, it is effectively a "short".
If one connects an ammeter across a low resistance voltage source (i.e., across the car battery) the ammeter will appear as a short circuit to the battery, and one or more bad things will happen. The 'least bad' will be blowing a rather expensive fuse in the ammeter that protects it from this kind of accidental use. Several of the "most bad" will involve hot molten metal and/or extreme heat.
Yes. My first comment on this thread says not to do that, and suggesting an alternative is "Ammeter between a battery's terminal and the car's electrical system." instead. https://news.ycombinator.com/item?id=35514652
I was replying to "anywhere near large enough capacity" in the next post. The typical 10A range is massive overkill for typical parasitic loads in a car, and even things like the fuel pump deciding to kick on and run in most cars.
[1]This is just what I would do. Only do this based on a reputable guide if you don't have experience working around car batteries.