Most of the car ammeters you get have positive and negative current - one to show charging, the other to show discharge. It's far, far more useful to have the ammeter pretty much where the fusible links are, with the only thing not going through it being the wires to the amp.
You know the amp is drawing current, you know it's a lot, and it fluctuates all the time, so seeing a waggling needle doesn't really tell you much. You want to know if the alternator and battery can keep up with the load over a longer period of time. So, if you put it where the fusible links are, you can see if the alternator is keeping up with it, which is what is important. Your voltmeter will tell you if the battery is getting screwed over.