Sorry I meant to say SPDT.
You seem to have the relay pinout wrong. It's right there on the case. Coil = 85-86, polarity probably
does not matter. Put the voltage source for the horn on pin 30 and the horn on pin 87.
Appears to take 14V on the coil to pull in the contacts [12V will likely work], and as mentioned last time,
you'll need a transistor driver, so see the link I gave.