Well, it's not that difficult if you have a wiring diagram, but the airbag
does complicate things a bit.
This wiring diagram may help him (you'll have the "with SRS" layout):
I'd start by grounding the horns directly to see if they come on. It's
likely a relay or ground problem due to corrosion at the connectors. You
/may/ be able to access the horns without removing the front bumper by
removing the plastic undertray.
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