The wire going to the stock horn is not large enough to run that small compressor. Use the stock horn wire, as was said, as the trigger wire for the relay.
Run 10 gauge with fuse from the battery to the relay (terminal 30 on the relay),
Most aftermarket relays use the same numbers:
30 - power in
87 - power out
86 - control current in (activates the relay)
85 - Ground
I usually just loop a short piece of wire from the ground terminal (85) back up to the screw to mount the relay
terminal 87 to the compressor power wire (10 gauge)
terminal 86 from the stock horn wire.
from the crocodile Dundee movie scene where he says "that's not a knife, this is a knife"
I say that's not a horn, this is a horn, LOL (my 2 Hadley air horns behind the grille in my 17 Frontier):
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My name is Tony and I'm a Infamousaholic
Current truck - 2017 Nissan Frontier Desert Runner ,
(formerly owned: 1993 Nissan Hardbody king cab 2wd, 90 Nissan Sentra, 94 Nissan Pathfinder SE 4x4, 05 Nissan Titan, 87 Nissan SE-V6 4x4 king cab, 94 Infiniti Q45t & 80 Datsun 310GX )