Adrian, you could try swapping the two horns, and throwing away the one that
no longer works (if that's the case). A used horn from a junkyard will only
cost you a couple of dollars. While you're at it, replace the original horn
with one from a big American car. The Isuzu horn is wimpy. If you don't have
access to a junkyard, any auto-parts store will have a generic horn in
stock.