Horn Diagnosis
Thread Starter
Old(s) Fart
Joined: Mar 2007
Posts: 50,768
From: Northern VA
Horn Diagnosis
OK, I'm officially tired of typing this same thing all the time. Now it's a sticky. There are only four steps needed to diagnose a problem with the horn. DO NOT replace any parts until you do this.
1) Verify that there is battery voltage at the threaded stud on the horn relay. If not, find the problem in the red wire from the battery.
1A) Verify good ground at the horn where it bolts to the core support. Temporarily run a ground wire from the horn to the battery negative terminal. If this fixes the problem, correct the core support ground issue.
2) Disconnect the green wires at the horns and run a jumper from each horn to +12V on the battery. Does each one work? If not, replace the horns. If it works, reconnect the green wires.
3) Disconnect the green wire at the horn relay. Jumper this wire to +12V. Do the horns work? If not, find the problem with the green wire between there and the horns. If it works, reconnect the green wire.
4) Disconnect the black wire at the horn relay. Jumper the relay terminal to ground. Do the horns work? If not, replace the horn relay. If the horns work, find the problem in the black wire from there to the horn button.
1) Verify that there is battery voltage at the threaded stud on the horn relay. If not, find the problem in the red wire from the battery.
1A) Verify good ground at the horn where it bolts to the core support. Temporarily run a ground wire from the horn to the battery negative terminal. If this fixes the problem, correct the core support ground issue.
2) Disconnect the green wires at the horns and run a jumper from each horn to +12V on the battery. Does each one work? If not, replace the horns. If it works, reconnect the green wires.
3) Disconnect the green wire at the horn relay. Jumper this wire to +12V. Do the horns work? If not, find the problem with the green wire between there and the horns. If it works, reconnect the green wire.
4) Disconnect the black wire at the horn relay. Jumper the relay terminal to ground. Do the horns work? If not, replace the horn relay. If the horns work, find the problem in the black wire from there to the horn button.
Last edited by joe_padavano; Nov 25, 2025 at 07:04 AM.
Thread Starter
Old(s) Fart
Joined: Mar 2007
Posts: 50,768
From: Northern VA
OK, I'm officially tired of typing this same thing all the time. Now it's a sticky. There are only four steps needed to diagnose a problem with the horn. DO NOT replace any parts until you do this.
1) Verify that there is battery voltage at the threaded stud on the horn relay. If not, find the problem in the red wire from the battery.
2) Disconnect the green wires at the horns and run a jumper from each horn to +12V on the battery. Does each one work? If not, first verify a good ground and if that doesn't do it, replace the horns. If it works, reconnect the green wires.
3) Disconnect the green wire at the horn relay. Jumper this wire to +12V. Do the horns work? If not, find the problem with the green wire between there and the horns. If it works, reconnect the green wire.
4) Disconnect the black wire at the horn relay. Jumper the relay terminal to ground. Do the horns work? If not, replace the horn relay. If the horns work, find the problem in the black wire from there to the horn button.
1) Verify that there is battery voltage at the threaded stud on the horn relay. If not, find the problem in the red wire from the battery.
2) Disconnect the green wires at the horns and run a jumper from each horn to +12V on the battery. Does each one work? If not, first verify a good ground and if that doesn't do it, replace the horns. If it works, reconnect the green wires.
3) Disconnect the green wire at the horn relay. Jumper this wire to +12V. Do the horns work? If not, find the problem with the green wire between there and the horns. If it works, reconnect the green wire.
4) Disconnect the black wire at the horn relay. Jumper the relay terminal to ground. Do the horns work? If not, replace the horn relay. If the horns work, find the problem in the black wire from there to the horn button.
Registered User
Joined: Mar 2026
Posts: 3
Sticky...but good
This is crazy Joe, I literally joined this forum 2 days ago...intro'd myself and my 59 Dynamic 88 named Baby Dy in the Newbie thread, and stated I was having horn and turn signal issues. This thread is my first in researching my horn issue and your post is the first one I read. I have done all your suggested steps to isolate problem except isolating black ground wire at horn relay (step 4). I do believe this is where my problem lies since all other tests were good. Thanx dude...I knew somebody out there had an answer.
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