[HarryD]

Ulrich,

When I get to a place like where you are, I go back to basics.

I am assuming the relay socket is wired it at this point.

1-Disconnect your battery.

2-Use your continuity tester to verify that your socket has:
a-Continuity between the battery and pins 30 and 86 of the socket. Check the other 3 pins to verify no continuity.
b-Continuity between pin 87 and ground (with the horns in the circuit, the resistance will be greater than 0 ohms) and no continuity between any of the other pins.
c-Press the horn button and verify that you have continuity between ground and pin 85. When you release the horn button, the continuity should go away.

3-Unplug and check your relay to verify:
a-That you have coninuity only between pins 30 and 87a; and
b-pins 85 and 86.
c-There should be no continuity between any of the other pins.