Junction box 4 amp fuse problem

[72K10]

I think I've gotten most of my electrical problems fixed, but I'm still blowing the short 4 amp fuse between the battery and the junction box (small post on firewall next to battery). I've had the pickup 4 years and have never gotten the 4 amp fuse to work. Even after replacing the engine, alternator, regulator, battery, reworking the fuse box, new headlight switch, new horn relay, HEI, new dimmer switch etc., I still can't keep that fuse from blowing. I put a 30 amp fuse in it, and it works,but?? Any ideas?

Thanks,
Chris