I suspect that water in the passenger trunk well may have gotten into your module. You have to take out the foam blocks in the trunk to see, but it is a job because you have to take out some interior panels too. Another way to check would be to slide under the rear of the car and locate the rubber plugs in the bottom of each well. Pry them out and be prepared with a bowl to catch the water (so you will know how much you have pooled in the wells) If you find any water, fix the leaks and dry out your parts as described above.

You could even have a bad headlight switch. All these parts network, so the fault could be in an unlikely place.