Repairing a cracked trailer frame tongue: what a weld inspector would want you to do

This is the kind of weld where "it held when I kicked it" is not the test. The sequence: grind out the crack completely to clean metal, drill stop holes, V-groove to 3/4 depth, preheat, root pass with 7018 or MIG at full-penetration settings, fill, cap. Then weld fish plates (1/4" flat bar, ends tapered, not square) over both sides so the repair is not the weakest point. Grind nothing on the stressed side; the cap stays.

If the crack is at a tongue-to-frame junction on a trailer that will carry a car, have a shop do it or at least look at it. For a 4x8 utility trailer this is a solid DIY job.