@SStinger2k2 I’ve been sitting here wondering why you even need the bus tie. I was thinking you want to simulate failures and some advanced stuff with your home cockpit setup but I’ve realized you probably just want to toggle it closed (connected) so everything works on ground power without draining any batteries.
You should just install the flight dynamics mod, because they changed the bus tie to closed by default, and I suspect this is all you need (for now anyway). I’m guessing they did this for exactly this reason as well. Now that I understand the electrical system it’s obvious: external power only powers the right side of the plane, unless you open the bus tie. The standby battery isn’t listed on the MFD electrical but is draining unless the bus tie is closed (connected) or the APU is running or the left engine is running.
Edit: re-reading the docs I’m not so sure, they imply it was closed by default but I think it was open by default. Anyway consider this if it would help for your problem.