Sorting this out remotely is going to be slow and methodical so will have to be done over a few steps.View attachment 297992
It only trips when those 2 wires in the circle are joined. the arrows are the other ends of the same wires on each coil.
When the 2 are joined together it joins both coils together. all wires on both coils test for continuity.
Is there a possibility that they shouldn't be joined at all?
Could it be that the 2 single wires from each primary that go to the front switches should actually be double just like the other 2?
It could be that those two wires are the ends of on unused tapping. The transformer's out now so it would be a good time to do some checks with a test meter and see if you can work out what the winding configuration is.
If you have three separate wires coming from each end of the transformer, and that middle wire, I think you now have this :-
Set your meter to Ohms, connect one end to one of the X points and check identify the other other end of the X, label this wire X2. There should only be one. Then do the same with the other X.
Then check to see if the four unlabelled wires are separate windings - just connect your meter to the two wires at each side of the transformer and see if you get continuity.
Once this is done and you confirm we have the above diagram configuration, we can go onto the next stage which is identifying the phasing of the windings.