Look on the underside of the PCB.
The drawings are either in the Wiki where you looked (I think?) or can be downloaded via the link there.
The 5 V rail is common to the screw terminals, the USB & FTDI connectors and the battery. The 3.3 V rail can derive from that, or from the a.c. adapter if link JP2 is present. There is no mechanism to derive 5 V from the a.c. adapter.
Pin 5 is a switched output from the processor. It will always be less than the 3.3 V rail.
There’s comment about the temperature sensors here: DS18B20 reliability considerations - #25 by Robert.Wall