My guess would be a bad VTS control module. If I connect power to the VTS on my XP, it applies 12v to the MPEM. I'll hear a relay click up front and my low fuel LED comes on, and my battery drains, even with the key off. I disconnect the connector that supplies power from the rear electrical box to avoid the issue until I can replace the control module or more likely, go with my own VTS relay circuit.
If not the control module, then you've got 12v going somewhere it shouldn't be from somewhere else.