A1363 - should not really be an issue. But are there A2915 or A2916 in that same circuit ? That would cause problems.

Unplug J1 from the Rectifier board
Locate the two GI circuits. The colours will be

J1 - Pin 1 = GI BUS
J1 - Pin 4 = GI BUS
J1 - Pin 3 = GI Return
J1 - Pin 6 = GI Return

They will be paired off - so on the playfield there will be a colour denoting the GI BUS and the GI Return - easy to spot on the playfield. So by testing with a meter, you can find out which pair are shorted to Ground. Remember - GI Return is effectively Ground - So what you are looking at doing is a process of elimination with the GI BUS coloured wires - one of those is shorted to ground, and which ever is - that's the next part to figure out.

You can test with J1 inserted and the game off. Pins 3 and 6 will be shorted to ground. Pins 1 and 4 will not - so which is shorted to Ground ?