You can use the +5V and GND pins on the RS232 connector or other external pins that supply +5V (see the physical pinout diagram you can get from this site for alternative pins to get +5V/GND.) You would feed these two to the wind vane dual wiper potentiometer.

Anemometer connection to the AVR MT 128. The firmware is using INT0 interrupt for the anemometer counts. One line of the anemometer switch is connected to +5V and the other to Pin 9/INT0. I also added a pull down resistor to insure when the switch was open, the signal would be pulled down to ground. There are probably better ways to do this, but this worked well.

Wind vane wiper connections to the AVR MT 128 Analog to Digital Conversion (ADC) ports.

You need to attach one of the wind vane potentiometer wipers to the ADC1 pin of the ADC external header. The 2nd wind vane potentiometer wiper, attach to the ADC0 pin. These are rather arbitrary, but match the firmware and can be easily changed in the firmware if you need to use different ADC pinouts. In any case, because the wiper voltages will be dependent upon the exact voltage you supply to the potentiometer as well as the orientation of the mounted sensors, there is a table of voltage pairs in the firmware that you will need to calibrate according to your installation.

These are the physical pin locations of various breakouts of the ATMega128 on the AVR MT 128