Horn went off continually on sons truck. Battery cable was loose tightened that and horn stopped blowing but fuse blew . After that whenever I put in a new fuse and hit the horn it would blow so I have replaced horn and fuse, horn still doesn't work. Now when horn is pushed I can hear a click at the relay but that's it. I swapped in a known good relay and still the same thing. Any suggestions?

1997 F150 V6 5 speed manual

 

I would start with Check to see if the ground is being applied to the relay for the horn
- confirm the click is the relay contacts being activated by the coil

If you pull the horn relay, inside the socket you should get + VDC at pin #2

Picture of relay ( check that you are using the socket view not bottom of relay view )



Quick 1st test, meter on pins #1 & #2, see if you have + VDC without pressing the horn ( test if switch is stuck ).
If not, same meter test for + VDC, press horn, should have + VDC on meter, if not need to figure out if + VDC is not on pin #1 ( use another known good ground to test pin #1 ).

If this test good, time to bench test the relay.

apply + VDC to pin #1, ground to pin #2 and check for resistance over pin 33 & #5. Should be < 100 ohms resistance.