Voltage controlling apparatus and methods of calibrating a device

A voltage controlling apparatus includes a housing, an ammeter, and a voltage adjustment mechanism. The voltage adjustment mechanism is configured to be in electrical communication with a power source and a device, e.g., a vehicle contactor assembly. For calibration of the device, the voltage adjustment mechanism is configured to adjust a voltage being delivered to the device, and the ammeter is configured to display a corresponding current reading of the device in response to adjustment of the voltage to the device.