Tap the switched 12 volts that is already present to inst' panel.
To use the always hot wires to amp gauge creates always on battery drain. This is the difference in amp gauge and volt gauge designs. The amp gauge does not have a direct to ground path on black wire side. A volt gauge does. So volt gauge needs to be on switched on/off and ground ( like a light bulb or most anything else ). You would simply connect the amp gauge red and black together to delete that gauge.
