You sure you have the right connector? There either has to be a relay or someone wired one in somewhere else.
To identify the connections, do this:
(Hook up the horns under the hood)
You know which one is battery, it's hot
You need to find out which one is horns. Hook your 12V test lamp into the hot connection, check it to ground to be sure you get a light, then plug the light into either of the unknown connections.
If the light does not light, try the horn button. IF the light "lights" you've found the right connector, and the button works.
If the light comes on without pushing the button, go out and disconnect the horns, and the light should go out.
If not, put your probe into the other unknown connector and the light should light, if so, go out and unhook the horns to confirm. If the test above showed you the horn connection, once again push the horn button and see if you get a light. IF so, the button is OK, and you need a horn relay.