ign/gau fuse keeps popping

i have a 91 s 15 jimmy and the ign/fau fuse keeps blowing its a 20 amp i trieda thirty and it bows two. some how it is shutting my alternater off so my batery go dead. cn anyone help thank you

First of all, stop putting a bigger fuse in. All you will do is cause a fire.

Check the wiring for short of where the insulator is worn off going to the battery, the alternator and the starter.