You know, this happened to me recently. I had inadvertently installed one of my front running lights upside down in a bulb change. The drain hole was then on the top instead of the bottom. Light filled up with water, and popped fuses.
Anyway, I would remove all of the bulbs from the running lights. If you don't actually find the problem doing that, then do this. Put a new fuse in and see if it blows, If it does, then you have a wire shorted. If not, install a one bulb at a time untl the fuse blows. Then you'll know where your problem is.
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