Well if they are basically the same and the same polarity you probably have the right way but standard CAN should be 0-5V. So that's a little strange but at least consistent between the two buses.

If you're getting something on the general bus, how is that possible *without* the CAN-B bus working? There must be stuff going across those pins 2 and 13 with some kind of gateway between the two. Maybe monitor those pins whilst there is traffic like steering wheel button presses. Even with a multimeter you should see some small change.