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My 52' F1 has a standard single trumpet horn with the original 3 contact relay. The horn hasn't sounded in years, but just for fun today I cleaned the relay contacts a little, re-connected the wires, and gave it a try. To my surprise, a faint little peep could be heard every time the horn button was pushed.
There was just a single wire from the relay going to the horn. As this wire was in very poor condition, I replaced it with a length of #10 braided wire. I didn't see a ground wire, but there was a second curious loose screw with a little star washer on the horn. This screw and star washer looked a lot like the one I used for connecting the horn to the relay. Could this second screw be for a ground wire that is missing? I would think though, if the horn wasn't grounded, it wouldn't sound at all. Thanks.
The horn is grounded thru the horn mount bolt, the screw you are looking at is most likely the one that adjusts the pressure on the vibrating diaphram of the horn to raise/lower the horn sound.
Try taking the horn off and holding it trumpet-down. Tap around the base of the trumpet, see if dirt/bugs/nests fall out.
Then pop the dome off the back of it. Re-install. There is an adjusting screw in the middle, Try loosening it a little, blow the horn a few times, then adjust until it sounds good. Re-install the dome.
So, no surprise, there wasn't an easy fix. I cleaned up the contact points on the bracket and changed to new fasteners and washers--same weak little sound. I tried to follow Ross' advice--no bugs or dirt fell out. As to "popping off the dome"; that seems a little problematic. The back of my horn seems to be riveted. See pics below.
As the pictures show, there are some screws that could be removed, but the rivets seem to be what is really holding the unit together. Any further suggestions? Should the rivets be drilled out and replaced with screws?
The silver screw is the one I used for the connection to the relay. The screw at the center/top is the one I noted that appeared to be loose and had a star washer. I tried to tighten it, but it turned hard and I decided not force it all the way in. So yes, I did some adjustment to the extent that I tightened it a little. Is your horn riveted together like mine? Did you take yours apart? Thanks.
The horn is really sensitive to clean connections. I used stainless wiring hardware there to make sure it stayed rust free. Here is what my wiring looks like for your reference:
My horn was riveted like yours and sounded like you describe. I drilled out the rivets, took it apart and cleaned it up.
I have one power wire from the relay and it grounds through the mount. I made sure I had a good ground and I already replaced my wire harness. I had to use the adjustment to get it to sound good but it works great now.
I used screws to put it back together. New rivets would work too.
Be sure the horn is not mounted in a rubber isolater which would mandate a separate ground. I don't know if you have anything like that but I believe I've seen it.
Ray, The base of my unit has 2 attachment points that are not insulated. There is a third attachment point consisting of a metal band around the trumpet part of the horn that is bolted via a little bracket to the hood. This point is insulated. The ground, I'm thinking, is formed by the base attachment points.
I haven't gotten around to drilling out the rivets yet, but will be on that later today. Thanks everyone for your help.
Success! My horn just spoke to me. It was loud but maybe not necessarily pleasing. The contacts inside the horn were bad. They were pitted and covered in white oxidized material. With them cleaned up, my horn works again. The paper gasket material inside the horn and the thin metal disk are damaged, so the tone of my horn is probably not the best--but at least it is able to put out a loud sound. I was using a battery charger to test my horn. In the truck, with the current supplied by the relay, the horn may sound a little different. Thanks everyone for all your help.
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