All you can do is chase the short.
Disconnect the harness to the taillights that is near the middle of the bed and see if it kills the fuse.
If it doesn't the issue is behind that connector.
If it kills the fuse take the bulbs out of the front markers and turn signals. Still dead? inspect the wiring to the front lights. Mine was a disaster area.
Still no workie? Unplug the trailer connector if you have one.
Still bad? now you only have about 6-10 feet of wire to check.
Pro Tip;
Put a much lower amperage fuse that you have 937 of to check things. Also, when you find the short don't assume that is the only fault. Plug in one thing at a time with a low amp fuse in to make sure you find all the causes.
My wife's Astro did that to me last Fall. It ate the coil, module, and module connector at the same time.
I was kick kittens mad!