Hot horn
Thread Starter
Safety Car
Joined: Sep 2005
Posts: 4,226
Likes: 643
From: Orange County Ca
Hot horn
My horn works well when the car is cold. After the engine gets up to running temp and everything under the hood is hot (69 BB), the horn doesn't work or works intermediately.
My best guess is that the relay is going bad. I'll start checking from there first.
Are replacement relays any good? I've had a lot of problems with repo and rebuilt parts, and new china crap parts. Can these relays be serviced?
Anyone else have this problem? What did you find?
My best guess is that the relay is going bad. I'll start checking from there first.
Are replacement relays any good? I've had a lot of problems with repo and rebuilt parts, and new china crap parts. Can these relays be serviced?
Anyone else have this problem? What did you find?
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The horn relay is in a perfect place to catch all the heat.. I'd go there first. After that, check the ground from the steering column- it goes thru the rag joint. Easy to check-- just make a little jumper wire to go over the rag joint and give it a try.. Or if you have a meter, check resistance between the steering shaft just above the rag to the frame.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
My horn works well when the car is cold. After the engine gets up to running temp and everything under the hood is hot (69 BB), the horn doesn't work or works intermediately.
My best guess is that the relay is going bad. I'll start checking from there first.
Are replacement relays any good? I've had a lot of problems with repo and rebuilt parts, and new china crap parts. Can these relays be serviced?
Anyone else have this problem? What did you find?
My best guess is that the relay is going bad. I'll start checking from there first.
Are replacement relays any good? I've had a lot of problems with repo and rebuilt parts, and new china crap parts. Can these relays be serviced?
Anyone else have this problem? What did you find?
Thread Starter
Safety Car
Joined: Sep 2005
Posts: 4,226
Likes: 643
From: Orange County Ca
The horn relay is in a perfect place to catch all the heat.. I'd go there first. After that, check the ground from the steering column- it goes thru the rag joint. Easy to check-- just make a little jumper wire to go over the rag joint and give it a try.. Or if you have a meter, check resistance between the steering shaft just above the rag to the frame.
I opened the relay today and it looks good. I did clean up the contacts which are a little pitted. I took off all the connected wires and cleaned them even though they all looked ok. I'll check it all the next time I drive the car and get it hot.
Are you ever going to get back out here to SoCal for another birdrun?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Carefully straighten the retaining tabs on the horn relay cover and remove it. Clean all the contacts with fine wet/dry sandpaper (no more than necessary) and put a little non-conductive grease on them to prevent future contact arcing/burning. Replace the cover and use for another 40 years.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I've been out there a few times, but never had time for much. Worked the Orbis Flying Eye Hospital project- they retired the DC-10 and got an MD-10. The company I work for donated one of our retired DC-10's for interior parts. And then some stuff for 10 Tanker when they were at SCLA. Closest to there I've been the last couple of years is Las Vegas. And that's been infrequent and only a couple of days.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Carefully straighten the retaining tabs on the horn relay cover and remove it. Clean all the contacts with fine wet/dry sandpaper (no more than necessary) and put a little non-conductive grease on them to prevent future contact arcing/burning. Replace the cover and use for another 40 years.
?????
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Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
My horn works well when the car is cold. After the engine gets up to running temp and everything under the hood is hot (69 BB), the horn doesn't work or works intermediately.
My best guess is that the relay is going bad. I'll start checking from there first.
Are replacement relays any good? I've had a lot of problems with repo and rebuilt parts, and new china crap parts. Can these relays be serviced?
Anyone else have this problem? What did you find?
My best guess is that the relay is going bad. I'll start checking from there first.
Are replacement relays any good? I've had a lot of problems with repo and rebuilt parts, and new china crap parts. Can these relays be serviced?
Anyone else have this problem? What did you find?
heat=resistance=lower current=less magnetism=less pull in
Pits are normal. They correspond to craters on the other side. This actually improves contact patch. This is why you need a dwell meter to measure used points.
Cleaning contacts with contact cleaner is good. Any contamination is bad.
Dielectric grease is for flash over in HV work.
Le Mans Master
Joined: May 2003
Posts: 8,877
Likes: 3,556
From: Fernandina Beach FL
2023 Restomod of the Year finalist
2020 C3 of the Year Winner - Modified
I'd look at the horn itself-
It has a coil of wire inside and contacts that is also affected by heat-
Next time the horn is hot and working intermittent- unplug the green wire at the Horn relay and put 12+ volts to it-
If it doesn't work - you know the horn is the problem.
Richard
It has a coil of wire inside and contacts that is also affected by heat-
Next time the horn is hot and working intermittent- unplug the green wire at the Horn relay and put 12+ volts to it-
If it doesn't work - you know the horn is the problem.
Richard
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You'd rather have conductive stuff laying around an electrical device?? The purpose of it is to 'shield' the contacts from air when connection is made. Inhibits arcing and burning of contacts. Connections are made when the contacts actually touch.
Last edited by 7T1vette; Feb 10, 2018 at 12:50 AM.
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
You'd rather have conductive stuff laying around an electrical device?? Nobody said that at allThe purpose of it is to 'shield' the contacts from air when connection is made. Inhibits arcing and burning of contacts. Connections are made when the contacts actually touch.
Thread Starter
Safety Car
Joined: Sep 2005
Posts: 4,226
Likes: 643
From: Orange County Ca
Well, yea, 5:58 AM on a Saturday? Not many people to honk at that time. 
See you tomorrow at 8:00.
R&R'd the relay. It looked surprisingly good for 49yrs old. Minimal corrosion with a little pitting on the main contact. Even the external wire connections looked good. The 2 push on contacts may have been the problem. They are hard to clean, but a few on/off cycles seems to have helped. Maybe one of them was loose?
Anyway, seems to work now.
See you tomorrow at 8:00.
R&R'd the relay. It looked surprisingly good for 49yrs old. Minimal corrosion with a little pitting on the main contact. Even the external wire connections looked good. The 2 push on contacts may have been the problem. They are hard to clean, but a few on/off cycles seems to have helped. Maybe one of them was loose?
Anyway, seems to work now.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Depending on the model year of your car, the horn relay is also used as the 'buzzer' for the ignition key switch (key left in with engine OFF). That puts a lot of cycles on the contacts.
Thread Starter
Safety Car
Joined: Sep 2005
Posts: 4,226
Likes: 643
From: Orange County Ca
OK, update.
Did a 40 mile drive in 70 deg weather, so the engine compartment got up to normal/hot temp. No horn.
But I did find something. The horn doesn't work with the ignition switch in the run position when hot, but does work in the off position, even when hot. Weird huh??
So now I'm thinking that it's the switch?
'69 model
Did a 40 mile drive in 70 deg weather, so the engine compartment got up to normal/hot temp. No horn.
But I did find something. The horn doesn't work with the ignition switch in the run position when hot, but does work in the off position, even when hot. Weird huh??
So now I'm thinking that it's the switch?
'69 model
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
OK, update.
Did a 40 mile drive in 70 deg weather, so the engine compartment got up to normal/hot temp. No horn.
But I did find something. The horn doesn't work with the ignition switch in the run position when hot, but does work in the off position, even when hot. Weird huh??
So now I'm thinking that it's the switch?
'69 model
Did a 40 mile drive in 70 deg weather, so the engine compartment got up to normal/hot temp. No horn.
But I did find something. The horn doesn't work with the ignition switch in the run position when hot, but does work in the off position, even when hot. Weird huh??
So now I'm thinking that it's the switch?
'69 model
Le Mans Master
Joined: May 2003
Posts: 8,877
Likes: 3,556
From: Fernandina Beach FL
2023 Restomod of the Year finalist
2020 C3 of the Year Winner - Modified
OK, update.
Did a 40 mile drive in 70 deg weather, so the engine compartment got up to normal/hot temp. No horn.
But I did find something. The horn doesn't work with the ignition switch in the run position when hot, but does work in the off position, even when hot. Weird huh??
So now I'm thinking that it's the switch?
'69 model
Did a 40 mile drive in 70 deg weather, so the engine compartment got up to normal/hot temp. No horn.
But I did find something. The horn doesn't work with the ignition switch in the run position when hot, but does work in the off position, even when hot. Weird huh??
So now I'm thinking that it's the switch?
'69 model
IF so - that makes sense- the horn system- relay AND horns are seeing a higher voltage- almost 14 versus 12.5 when the car is not running.
The ignition switch has nothing to do with the horns-relay- wiring.
Like I said- jump the green wire to a 12volt source- the terminal on the horn relay will work fine. With the car off and hot-doesn't work- you have narrowed it down to the horn(s).
That will tell you if is a bad relay or the horn(s)-otherwise you are chasing your tail...
Richard
Last edited by Richard454; Feb 11, 2018 at 08:12 PM.