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73 dodge b100 horn not working
#732481 January 29th 2018 3:11 pm
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Can anyone help understand better as to how the horn wiring works on my 73 tradesman? My horn isn’t working, I have a lime green and black wire that is hot at the horn and a dark green and white wire that isn’t at the horn. I trace it back yo the firewall and it hot. I also am getting that it’s hot on the inside of the firewall but from there I’m at a loss. I take the cap off the horn and I see a black wire about 6 inches long that isn’t hot... that’s about where I’m at. I’m not sure what’s suppose to be hot and what isn’t or where to trace to from here. Just one of those small things that’s never worked that I would like to have working.

Thanks for any help.

Re: 73 dodge b100 horn not working
UncleRico #732482 January 29th 2018 4:12 pm
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The black wire that is six inches long is the horn wire. Try grounding it and see if the horn sounds. It should. If it doesn't sound then there is a problem elsewhere.

The wires at the horns should not have power unless the horn button is depressed. If the wires attached to the horns are always hot then either (a) they are the wrong wires or (b) there is a problem with the horn relay.

You need to locate your horn relay and see what is going on there.

The way the system works is the relay should have a constant hot feed. The relay will have three wires: a contant hot wire from the fuse box, the wire that runs out to the horns, and the wire that goes up the steering column and is the ground for the circuit. The horn wire grounds the trigger circuit in the relay which then sends the full current out the wire that connects to the horn. I don't have a shop manual old enough to tell you the colors of the wires, but some time with a test light and careful tracing of the wires going to the relay will get you where you need to go.


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Re: 73 dodge b100 horn not working
Reed #732483 January 29th 2018 5:02 pm
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I think there may be a problem with the horn itself. I took it completely out and ran 12v straight to it and got nothing. Is one of the wires to the horn a ground? Or are both intended to be hot when the horn is depressed?

Re: 73 dodge b100 horn not working
UncleRico #732484 January 29th 2018 5:10 pm
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What I’m not understanding is the fuse box is labeled radio-R/up and horn... both on tge same fuse. Makes no sense because it’s an ignition hot. So I have an ignition hot running from tge fuse box to a relay which also runs to the horn and blinker switch and the same fuse also powers the radio. From the relay the green wire run to the firewall plug and straight into the horn. The horn has a 12 volt hot but only when the ignition is on then a dark green wire that runs back through the firewall and up the column to the horn button. This wire is never hot. I’ve never seen or heard of a horn having an ignition hot.

Re: 73 dodge b100 horn not working
UncleRico #732488 January 29th 2018 9:18 pm
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The horn grounds through the horn mounting bracket. The wire going to the horn is only hot when the horn button is depressed on the steering wheel.

The horn should not have an ignition hot/switched hot lead. Has the wiring in your van been modified? Do you have a factory wiring diagram for your van? There should be a constant hot feed to the fuse box. A constant hot feed to the fuse with the horn. A constant hot feed going to the horn relay. Period. The wire that goes up the steering column for the horn is nothing but a ground. The last wire in the system is the wire from the relay that goes out to the horn. That last wire is hot only when the horn button is depressed.


Windows- they're what make a van worth owning!
Re: 73 dodge b100 horn not working
Reed #732499 January 30th 2018 1:25 am
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I need to get wiring diagram. This all seems to be untamperred with. The fuse is lable radio/horn snd is ignition hot. A green wire goes into a relay and out of the relay to the horn. This same relay has a red wire that run up the column to the blinker switch and operates the blinker. There’s a second wire from the horn up the column to the horn button. This entire system is ignition hot and appears to be factory. I’m mind blown that one fuse would be labeled radio and horn... the ignition hot is throwing me way off lol.

Re: 73 dodge b100 horn not working
UncleRico #732501 January 30th 2018 12:18 pm
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Don't know if you can get these big enough to read, but here's the factory diagram. Hope this helps
.

Attached Files P1010371.JPGP1010372.JPGP1010373.JPGP1010374.JPGP1010370.JPG
Re: 73 dodge b100 horn not working
UncleRico #732504 January 30th 2018 1:59 pm
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Update, horn is working. Never seen this before on any vehicle but I replaced tge horn with one that I tested good and it works now but only with the key on... an ignition hot horn... weird

Re: 73 dodge b100 horn not working
Sparkynm #732505 January 30th 2018 2:05 pm
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Thanks Sparkynm... That’s awesome, I appreciate the photos.

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