You can assign PWM-controlled devices which are connected directly to one of these mega2560 controller pins - from 2 to 13, and 44,45,46. In the Configurator, select the needed parameter for output and select one of these free pin.
Connect an ammeter to the PWM output of the controller through a current limiting resistor, with the other wire of the gauge connected to the ground. The resistor can be varied from 5 to 100 kOhm depending on the gauge you will use. You can select a suitable resistors by checking the range of the gauge needle. The simplest option you can use just one limiting resistor. Here are the connection options of the coil gauge:
You can use a 24-channel PWM driver (TLC5947) with CLK signal connected to one of these mega2560 controller pins: 30 - 39.
In the Configurator, click the PWM driver button, then select a free pin to which the CLK signal of the PWM driver will be connected. Two other control signals are connected to corresponding D and L signals of the system bus. +V is the driver powering input, you can either use +5v from the bus or connect another external power supply.
In this case when choosing a parametr for output in the Configurator, you need to select the PWM controller output number (currently only up to 16 outputs are supported in the configurator.
Unlike direct connection, the gauge's "+" output is connected to +5V, and "-" is connected to the signal, not to GND.