i bought a new ammeter and hooked it up per the wiring diagram: battery to the charging side of the guage; negative side of the guage to the voltage regulator. with the engine turned off, when i turn on the headlights, the ammeter shows that it's charging. shouldn't it be discharging? is the fix simply to reverse the wires? if so, why would the diagram have it backwards. this is a negative ground, 12 v, 1950 chevy half ton. thank you.