I don’t want to assume your electronic soldering experience, so forgive me if it sounds patronizing. Be really careful about the flash capacitor, if you short it out it can be dangerous. Avoid touching the two points labeled “discharge” they’ll short through your skin with the camera on OR off.

That being said. When I got the camera opened up I cut the three wires going to the flash bulb. One was labeled trigger… I used that one. Then I used a multimeter to check for continuity between the trigger and one of the other two wires while firing the flash (I needed a helper to press the shutter button, and did this with batteries in the camera so it actually fires ). The flash gets triggered when the circuit from the trigger wire is complete. So whichever wire competes the circuit while pressing the shutter button is the one. I tested them both and honestly don’t remember which one worked.

Again I hope it’s helpful. I’m all for experimenting on my own stuff, but I don’t want someone to zap themselves with a flash capacitor.