This is an old post so it may just help someones else looking for info.
Be careful cutting out your cars. The Comm boards ( located on each SBC) daisy chain from the B7 cab to each car in it's loop. The car Comm are GO1's except for the last cars in the chain which are G02's. There is an inline resistor network beside the two red jumper plugs. If you have a machine room with multiple com loops you will have more than one.
That end of the chain comm board needs to be moved to the next car
as you take it out. Start with the last car in the chain first.