Thanks for your post.
I did respond on your other thread, but here's the same response for this thread....
What you are measuring there is a 'trailer detection' voltage - TowPro does put out a low voltage to sense for a trailer/brake magnet connection and when it does, the circuit will load down to 0V.
You can test this by connecting an automotive test light (needs to have a 21W bulb in it, no LED's) and testing the unit per the following procedure.
TowPro draws very minimal power when in this standby/sleep state (less than 5mA), so all normal by the sounds of it!