Reply To: What are the empty holes next to the GPIO header on an old Pi model B?

We still have a few of these on line counters, so I’ve been through it.

P6 is the RUN pin. Shorting its two holes resets the board, so solder in two header pins and wire a normal momentary push button across them. That’s your reset button, nothing else needed.

P5 on a rev 2 board is extra power and GPIO:

P5-1  5V      P5-2  3.3V
P5-3  GPIO28  P5-4  GPIO29
P5-5  GPIO30  P5-6  GPIO31
P5-7  GND     P5-8  GND

GPIO28/29 can be a second I2C bus. It’s meant to be fitted from underneath, so pin numbering looks mirrored from the top, the square pad is pin 1. For a temperature logger you don’t need P5, use the main header (a DS18B20 on GPIO4 is the easy one). Everything is 3.3 V logic, never 5 V into a GPIO.