help

. I was checking my lights this evening. Everything worked apart from the rear fog light. Checked the fuse, it was blown. put a new fuse in rear fog light worked. started engine fuse blown again. I put a 25amp fuse where before was a 30amp. In the wiring manual it says that the fuse powers the dip beam,no plate light and off side tail light. when the fuse blows they still all work. any ideas?
Thnx