The Stovebolt Site Forums The Shop Area The Electrical Bay 1950 3100 horn

I can't remember, but are the horns on earlier AD trucks (without horn relays) supposed to be isolated from grounding through the mount? Or to put it another way, is it ok to have the horn body grounded? I ask because my horn worked perfectly when bench tested but when I mounted it using a mount I fabricated it no longer works. My DIY mount does not prevent the horn from grounding threw it so I am wondering if that may have damaged the horn?

Your horn has two wires going to it. The Positive one is always hot. The ground wire goes to the horn button. The horn guts are isolated from the body of the horn. If they were't, the horn would blow all of the time or the horn would catch on fire.
I suspect that there is a problem with a break in the ground wire or the horn switch is bad.
Check for battery voltage at the hot wire at the horn to rule that out first since that is easy to do.

It was hooked up correctly and like I said tested on the bench and it worked fine. When it was installed on the truck I even tried running a jumper to ground in place of the horn switch and that didn't work either. I have done automotive electrical work for decades so I have a fairly good idea what I am doing😉. Hooked up on the truck exactly the way it was on the bench, the only difference being it was grounded through the mount to the engine. Now it no longer works not even on the bench???

Its been a long time since I had my last all original AD truck so my memories of this are vague at best. Do the horn mounts have some kind of isolators in them so the horn attaching bolts do not ground through the bracket? It sorta looks that way from these pics but I am not sure.

The horn mounts don't isolate the horn from ground electrically, they just have a design to isolate the horn from engine vibrations. The horns are electrically isolated internally. Carl already said that.

Are you sure you have power to one of the horn wires? If you don't, then the horn won't sound even if you supply a ground to the other terminal. Check with a voltmeter.

As I said now the horn will not work even hooked directly to a battery on the bench. Looks like maybe it was a fluke that the horn failed the first time I tried it after installing it. Strange though as it had worked just fine only a few minutes before on the bench.🤷🏻‍♂️

Just a thought, but the horn looks to be an original 6 volt type. From my reading of your signature line posts, I believe your truck has been converted to 12 volt. Could be the voltage slagged some thing in the internals of the 6 volt horn or it just gave up.

You might read through the info (and somewhat comedic comments) of Bolter "bartamos" in his reply to a similar on-topic thread.

I'm pretty sure there are other existing threads that discuss disassembly, cleaning and repair of these horns. If you can't locate one of those old threads yourself, let us know and someone can try and find one that may help you go down that road.

Ii didn't see that you tried bench testing it again. You can see if it burnt out as Dan suggested by measuring across the two terminals with an ohmmeter. If it shows an open circuit, then the coil inside is toast. If you're really handy, you could rewind the coil, but that would be a pretty big task.

LOL! What bartamos is describing is known to us Mechanical Engineers as "Percussive Maintenance".

Checking the coil was one of the first things I did and it has resistance so that is good. I suppose it could be the points/contacts need cleaning. I'm going to do more inspecting when I get time.

Cleaned the points readjusted the nut that breaks the points contact, and it works again! I would like to thank you guys for your input ☺

Glad you were able to get it going again, and thanks for posting the solution to the issue.

TOOT TOOT !!