It is for sure "interesting." I've had friends with older Ford pickups, and have owned 2 Rangers, 86 and 87, and both ammeters were quite "numb", (insensitive.) When you sat, engine off, and turned on the headlights, you had to look quite closely at them to see if they moved!!! ALL external shunt ammeters that I know of, GM, Chrysler, Ford, used the harness as a shunt, so the wire gauge and length of wire affected the sensitivity of the ammeter