A truck and trailer thread.

[McMXi]

Ahh, well then that's some good detective work!! Failed horn relay or blown fuse are all possibilities!

More detective work this morning. The #37 15A horn fuse was indeed blown so I replaced it. I turned the ignition on, pushed the horn control on the steering wheel and the horn(s) sounded but weren't very loud. I pushed the horn control a couple more times and the sound decreased and then nothing. The fuse had blown again.

This indicates that the problem isn't with the clock spring but rather a short in the horn circuit which is most likely indicative of failed horns (shorted). There's a process in the factory repair manuals to troubleshoot horn related issues so I guess I'll be following that. The horns are cheap but access to them on the passenger side is a pain just like access to the ICM/IDM on the driver's side. They're protected by fender liners that don't really want to come out.

With any luck I can get the horns and cruise control working properly once I've figured out where the short is. Then I'm done for this winter with the F-250 since everything will be working fine so I can just focus on typical maintenance and regular trips to the car wash to get the salt off.

 

[biketopia]

Thats good news! We have seen the horns themselves fail and or draw a large load. It does stink they are buried, if you can unplug them and just hook a test light to it and hit the button a handful of times, that may lead you to a wire vs horn problem.

I just thought of this, it's also possible the relay is just getting shot and has dirty & burnt contacts and over overloading the circuit. Locate the relay and pull a similar one from the fuse box, and honk the horn a handful of times & see if the fuse blows again. Maybe you won't have to dig in as deep as you thought!

 

[McMXi]

I solved the horn issue! I figured that a short in one or both of the horns was the likely culprit so I removed the passenger wheel well liner and removed both horns. I used a 15A fuse in series on one of the terminals of each horn and powered each one from a 12V power tool battery. One horn worked fine and the other immediately burned the fuse. Turns out the cleaner looking horn has an internal short. I did measure resistance across the terminals but they were both around 2 ohms so not sure how else to confirm that one horn is bad other than by my Mickey Mouse "waste a fuse" test.

I rerouted the wiring harness from inside the fender to the engine compartment and plugged the good horn into the connector and the single horn now works without blowing the fuse. I need to be driving above a specific speed for the cruise control to engage so will test that feature tomorrow when I head to town. I have no doubt that it'll work fine, since as I mentioned earlier, it's on the same 15A fuse as the horn.

I plan on going aftermarket with replacement horn(s) and not installing them inside the fender well where they're concealed by the liner. It's a pain to access them there so will make a custom bracket and relocate the horns to the engine compartment away from heat and moving parts of course. If anyone has any recommendations on better (nicer/louder/cooler) horns then let me know.

Not bad for a 24 year old truck! The rear driver's side door rattles a bit on bumpy roads so that's another minor gremlin to address, but overall I'm pleased with how this truck is running and driving, and it allows me to keep the '24 F-450 out of all of the crap that winter provides.