i don't understand how you have it connected.
if the scanmaster is powering up, and only showing 2.2 , then you are not getting data from the powerlogger.
the data wire is the white one, and it needs to be connected to the SCM terminal of the analog connection unit of the powerlogger. The analog unit needs to connect to the PL using the gray analog cable.
If all of this is connected properly, and the PL is installed properly, and the PL is functional. then you should have data.
I have never tried to probe the data wire with a test light, it might light it dimly. Its a pulsing 5 volt signal.
Can you post some pictures?
Bob