Wow this vehicle is really starting to break down.

Today ... vehicle sitting in the parking lot at work ... the horn started honking for about 20 minutes... just one long, straight "HOOOOOONNNNNNKKKK"

Coworkers came running into my office telling me my truck was going crazy in the parking lot. By the time I got there it had died. No more horn.

Truck runs, everything seems "OK" ... but no horn.

Fuse under the hood was blown so I replaced it. Now the relay under the dash will click ... but no horn.

If I sit there pushing it ... it will blow the fuse again.

 

You might check if the fuse that is blowing is in the circuit that activates the horn relay or the power to the relay that supplies the horn itself. Simple thing if you pull the wire off the horn and the fuse doesn't blow , the horn itself may be melted internally and shorted.

 

Thanks Hanky,

Following your advice, I have done the following:

- Removed the horns from the circuit (unplugged them)
- Replaced the fuse under the hood
- Multimeter - tested for continuity at plug (short circuit) = none
- Multimeter - tested for DC voltage delivered to plug on horn activation

When activating the horn I get a clean 12.5 volts delivered to the connector ... I can hold the horn as long as I want and it will not blow anything... so I figure wiring is good from the steering wheel all the way through to the connector.

Next up, I tested the little wiring adapter that's on the two horns themselves ... same battery of tests ... clean all the way through for as long as I want to hold the horn down

Next up, I reconnected each of the horns (one at a time) while I had my multimeter connected to the 2nd position... still have clean 12.5 volts delivered to the horn adapter wiring... and each of the horns "tries" to make a sound... but fails.

So... here's what I conclude... for whatever reason they are toasted... and by themselves (each one) they don't draw enough current to overload the circuit ... when when they are both trying together ... that's what must be drawing too much power...

So I'm order a new set of horns...

Fingers crossed.

 

The horns arent 100% duty cycle by design. It constant ON, they'll implode and overload..
Is this an XLT, or XLS?

The reason they initially were under constant activation needs to be diagnosed. Meaning, the activation voltage had to come from somewhere...

If XLT..
The horn function is through the Central Security Module. The integrated horn relay may have fail issues, or, the internal micro processor for relay activation. By removing the horns 'load' meaning unplugged, the relay/processor may not respond the same for a fail situation. Doubt horn buttons would be issue since the horns activated after you left the rig. If it were harness chafe, failed horn issues etc, the fuse would/may blow, more so now.

If XLS..
Possibly the serviceable horn relay, or, a grounding/control issue for the relay e.g sliding contact or horn buttons. Relay and buttons could stick, but generally don't apply themselves.. Being it they came in by themselves, I'm guessing n XLT....

 

Some horns have an adjustment. It looks like a serrated screw head. If your horns have that adjustment , stuff a rag into each horn and provide power and ground to each one separately while backing out the screw. Many times this will permit the horn to operate and adjust accordingly to get desired sound. If your horns don't have this adjustment, replacement may be the only option. You may still need to determine the cause for them coming on by themselves as Hayapower suggested.