Tail/horn fuse

I’ve been chasing a gremlin that randomly blows the “Tail/Horn” fuse on my Duster. It’s a 71 wiring harness.
Is a 20amp fuse big enough for this circuit? I can’t find anything on sizes of fuses.
My horn contact ring in the steering wheel is screwed up so I have the horn relay unplugged. This is why I don’t think it would be the horn circuit blowing the fuse, but I cannot find anything wrong with the harness to the marker lights or running lights. I’ve removed the entire front and rear harnesses and carefully inspected every wire that has anything do to with lighting. It all looks pretty much brand new.
I’m tempted to put a jumper wire in the fuse box and see what melts first, just so I can find this thing that’s cost me about 1 fuse per 100 miles. But I’d rather not.
Any ideas?
Thanks