Actually, if the coupler keeps opening only when connected, but not when disconnected, time to look at wiring. I'd look for chaffed wires that are momentarily being grounded, that's an issue that I see on occasion. If you don't address it, it can do a lot more damage. A high resistance joint won't cause the coupler to open as a rule.
The coupler has PV on one lead and the other is pulled to DC common to fire the coupler. Note that DC common is NOT frame ground. If the coupler control wire is grounded, a ton of current can flow through the coupler, and if continuous it can take out the board.
