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