1998 GMC 3500 - Fuse blows

my fuse keeps blowing out it my turning signal

Shorted bulb would be the first place I’d look. I have seen some pretty heat toasted connectors for the drl, maybe related, do not know for sure. Can you pinpoint it to left or right side?

First place I would look is your “trailer wiring” back by the hitch, it probably has rub a bare spot on some metal.

yep, check the trailer wiring and check the rear t/s bulb sockets. I’d just about bet money that they are pretty burnt looking.

battery + --------- fuse — turn switch ---- turn signal bulb ---- chassis ground.

There’s an electrical path somewhere after the fuse that’s connecting to chassis ground. You’ll have to disconnect stuff here and there until it goes away, then you’ll know it is something you disconnected. Test gadgets are available which make finding the location of the short circuit a little easier.