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Hello & Welcome,
This sounds like a very interesting issue.
From what you have said, I would suspect that there is a Ground issue. I have looked at the schematics for both the blower control and DRL (Daytime Running Lights) circuits, and they BOTH use a Ground circuit called G200. If the ground is not connected at the frame, and then connected through various wires and splices, then this kind of issue could happen.
Do you have a multimeter that you can use to make some measurements?