I recently had a similar issue on my 34 Performance which I came across when adding a battery monitor few years ago. I can’t remember the exact situation or cause, but I definitely had similar issues of lights not working, or only working on one side during the installation process.
I think it relates to the way Dufour had done the negative wiring and not all are led to same the house side of the wiring, and some go to the engine side. The house side negative post on the 34 is impossible to access behind the chart table shelves so I couldn’t test it but I think you may no longer have a common ground between the engine and house batteries – something to test to see if it resolves the issue for you.