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Horn Test

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ltcmikem

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The stock horn on my '49 GMC quit working and I'm trying to isolate the problem to the horn or the wiring/horn button. I know the horn is "hot" and the horn button provides the ground that activates the horn. But, my electrical troubleshooting is weak. I can't figure out how to test the horn. There are two wires going to two contacts on the horn and both contacts/wires are test "hot" on my multimeter. I considered grounding one or both of those two "hot" contacts on the horn, but I'd sure hate to do something stupid and fry the horn. Bottom line... how do I test the horn? Thanks in advance,

Mike M
'27 Chevy
'41 John Deere B
'49 GMC FC-150
 
1st. thing : throw the meter away ! it is useless for 99 % of automotive testing .

Not really throw out just donlt use it for lighting and horn tesing , stuff that involves loads .

Nowthen : at the base of the steering column in the cab you'll find a wire coming out of a small hole , unplug it from the harness and ground the harness end to a known good ground ~ this means a long bit of good wire like some old Zip Cord from a lamp or TV set with an big alligator clip on one end and a small one on t' other end , connect the big clip to the ground post of the battery and touch the little end to the wire ~ the horn should toot , it may just spark a little bit , if so , whack the cast part of the horn with a big heavy plastic screwdriver handle and try again .

You can also try brushing the ground to one of the terminals on the back of the horn , one side will toss big sparks and t'other will make it toot .

If you decide to fiddle the horn's adjusting screw ~ BE GENTLE ! 1/4 turn is a _LOT_ and one full turn can wreck the horn beyond all repair .

Some horns have a removable sheet metal cover so you can look at and file clean , the points therin .

DON'T mindlessly fiddle with the horn untill you know if it'll toot of not .

I hope this helps , I'm beat and totally stressed out .

-Nate
 
Here's what I would do...

Disconnect both wires from the horn. Remember which one goes where although it probably doesn't matter. Then use your voltmeter to see which one is hot (has 12 volts on it). My bet is only one will be hot when you check it this way. You would see 12 volts on both when connected to the horn because the 12 volts comes in on one and goes out on the other looking for a way to ground through the horn button.
Now connect the hot side to one of the horn terminals and run a wire from the other horn contact. Use the unconnected end of this line to find a place to go to ground on the chassis or engine to see if the horn works. If it does, the problem will be on the side going to the horn button or from the horn button to ground.
You can do a similar test on the horn button if you can find the two connections. One side should have 12 volts on it and the other side should go to ground when you punch the horn button. If one side has 12 volts, try touching it to something grounded under the dash, it should sound the horn. If that works, then the trouble is on the side of the horn button going to ground. You can try jumpering from the horn button ground terminal to ground and pressing the horn. If that works, then the problem is on the end where the wire connects the horn ground to the ground for the vehicle. If jumpering the ground to a good ground doesn't allow the horn to honk, then something is wrong in the horn button.
I hope that gets you going.
 
Nate & Bossman -

Many thanks for your responses. Both have good info to get me pointed right and together I have a solid understanding of how to proceed on the troubleshooting.

Mike M
'27 Chevy
'41 John Deere B
'49 GMC FC-150
 
When it comes time for a horn on one of the trucks we're doing we just grab one, gouge the bracket into the negative post on a test battery and hit the hot terminal with a jumper wire from the positive post. If it honks we bolt it on and if not we grab another one. The wire running up to your horn switch(button) is a ground wire for the horn relay--not a hot wire. When you push the button it grounds the relay so the contacts close and current is sent to the horn.
 
Hey you had it right on the wiring. A lot of times the horn with double terminals is used for twin horn setup where a wire from the second terminal passes across the the truck to a second horn on the other side. This makes it just need one wire from the relay to the first horn.
 
RE: Horn Relays

Please to remember : many of these trucks came without any relay so the contact ring in the mast jacket takes a beating , simply polishing it and then greasing it will return to as new function in most cases .

_always_ use (add) a relay if you're going to use two horns ("FanFare" setup)

6 volt horns will toot great on 12 volts unless you like to lean on it for a long time....

-Nate
 
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