I haven't needed to check the cabling so I don't really know. I would assume you would have to find and trace the cables and visually inspect them for damage. You originally suspected the PNP switch, have you ruled that one out? I think this advice here might be relevant for you: https://www.matthew...

strange they both failed at the same time. But at least you have a reason for them not working. It is hard when both fail at the same time. I had an issue with both low headlight beams on a friends car going out. Spent a while figuring it out to find both bulbs were failed!

Good Luck!

Neil.