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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.


Windows- they're what make a van worth owning!
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.

Re: 73 dodge b100 horn not working
UncleRico #732507 January 30th 2018 2:53 pm
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I stand corrected on several points. It appears your horn does have a separate ground wire and it is a switched circuit. I was looking at a 1982 Dodge truck wiring diagram and I wrongly assumed the wiring for the horn circuit would be the same as your van. My apologies for any problems my bad advice caused.


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Re: 73 dodge b100 horn not working
UncleRico #732513 January 30th 2018 9:23 pm
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No problem, Could you see the pics. alright? Got the FSM so if you need anything else, let me know! I'm hoping mine is just the horn also , don't think I have anything funky in the wiring either! HONK ON!!

Re: 73 dodge b100 horn not working
Sparkynm #732517 January 31st 2018 1:52 am
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Your images will certainly help me! To say my dash wiring was modified is modest, a previous owner dremeled a hole in the dash to run new gauges...shame he didn't have this diagram. Lots of tapping hots from odd places instead of the fuse box...

Also, to anyone with horn problems, there's a neglected point of potential under the steering wheel. That green hot wire comes up to a spring loaded roller contact, which makes contact with a metal ring plate behind the steering wheel. The contact rolls along that ring as the wheel is turned, always in contact. The ring is where that black wire under the horn cap goes.
The roller can wear and eventually lose contact.
So if you read hot at the harness connector but not at the black horn wire, that's the likely failure point.

Last edited by Miyagi; January 31st 2018 2:02 am.
Re: 73 dodge b100 horn not working
Miyagi #732522 January 31st 2018 5:03 pm
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Originally Posted by Miyagi
Your images will certainly help me! To say my dash wiring was modified is modest, a previous owner dremeled a hole in the dash to run new gauges...shame he didn't have this diagram. Lots of tapping hots from odd places instead of the fuse box...

Also, to anyone with horn problems, there's a neglected point of potential under the steering wheel. That green hot wire comes up to a spring loaded roller contact, which makes contact with a metal ring plate behind the steering wheel. The contact rolls along that ring as the wheel is turned, always in contact. The ring is where that black wire under the horn cap goes.
The roller can wear and eventually lose contact.
So if you read hot at the harness connector but not at the black horn wire, that's the likely failure point.


What year is yours? I know exactly what you’re talking about but mine isn’t ever hot. I was under the assumption that it was a ground that when depressed and made contact it grounded and completed the circuit.

Re: 73 dodge b100 horn not working
UncleRico #732528 January 31st 2018 5:58 pm
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Mine is a 74, and if I remember the diagram appropriately, for me, anyway... The power flow is battery + --> ignition switch RUN and START (I think. Definitely RUN) --> fuse box HORN/RADIO/B-UP --> the horn itself --> horn switch. The switch makes chassis ground via the steering column when pressed.

In Key RUN, you should be able to touch anything cab-side of the firewall plug to ground and get a spark and usually a toot. If you're between the firewall plug and the fuse box, it should still be sparky, but you're cutting out the horn.

I lost my horn switch, so have a spade connector just free hanging-- for awhile, it hung in such a way that bringing the turn signal lever down, it would touch the lever in the middle of the arc of motion and TOOT for a spit second.

Re: 73 dodge b100 horn not working
UncleRico #732870 February 07th 2018 11:31 pm
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My 1979 b200 is the same key off no horn


1979 Dodge B200 wrangler factory authorized van conversion.
360 cid 727 auto trans NP203 full time 4 wd
Re: 73 dodge b100 horn not working
UncleRico #738338 July 16th 2018 7:43 pm
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I have a 72' dodge van, key on for horn. I installed horns in the rear many years ago using a head light high/low beam floor switch. I installed it next to the floor high/low beam switch that was wired strait from the battery. The reason was, i wanted to be able to toot with the key off because many times I would have to alert someone for backing in to me while I was sitting in a parking lot. You are right the steering wheel horn is operated by it's grounding while pushing the center button. There is a roller wheel on the blinker control for the ground that sometimes may need a little cleaning along with its copper contact on the wheel it's self. Info: Most of these older autos need all the grounds removed and cleaned for an improved connection, specially on the computer ones.

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