Just for future reference if anyone is working with an old Faria tach like this thread shows, there is an internal PCB with transformer, diodes, caps, etc. so you can't expect to drive it via the external connection points provided to hook up to an engine. It works based on the current flow through the positive power supplied to the ignition coil on the engine. You can read more about the design by searching Google Patents for US3005155. You have to pry open the case and disconnect the meter movement from the original electronic package and then work directly with the meter movement itself.
The meter movement is a "taut band" design movement that works as an ammeter, and will read full scale with somewhere between 0.650 mA and 1.000 mA.
I was able to drive it directly by the Arduino to full scale using a PWM pin with a 10k / 10K voltage divider. The duty cycle number has to be limited to 250 or so in order to ensure you still have pulses - at 100% duty cycle (255) the meter will drop to zero.