I bet you've figured this out already and the creeek in my neck is for no
good reason. However, it appears that it is mounted with a cluster of relays above the interior fuse box (1 o'clock position). I suspect it's the
one of three relays nearest the driverside fender and fuse box. Most likely the smallest one closest to you.
To make positive ID of the relay, rest your finger next to the realy while activating the horn. Assuming the relay coil is good, and it's just a bad contacts, you should feel the relay activation.
I'd remove the nut or nuts holding the relay bracket in place to remove the horn relay if that's your intent.