1977 2500 M horn not working
Discussion
The horns have stopped working on my 1977 2500M. They were weak when I got it, it has been sitting for over a year, now they're dead. The horns themselves test fine. The owners manual refers to an inline fuse behind the carpet in the drivers footwell. Unfortunately, the '77 2500 M has its console where that area used to be on earlier 2500Ms. Any idea where the horn fuse is now located?
Can anyone provide diagnosis procedure or information for me to trace my problem? I supect it is a ground (earth) issue and understand there is a ground for the horn somewhere on the steering shaft...
I'm trying to get this car on the road and inspected. It's just about ready. I rebuilt the carbs, new fuel filter, will drain the tank and add fresh fuel. Once running and adjusted with horn working I can pass inspection and complete my registration.
Thanks for your help!
Can anyone provide diagnosis procedure or information for me to trace my problem? I supect it is a ground (earth) issue and understand there is a ground for the horn somewhere on the steering shaft...
I'm trying to get this car on the road and inspected. It's just about ready. I rebuilt the carbs, new fuel filter, will drain the tank and add fresh fuel. Once running and adjusted with horn working I can pass inspection and complete my registration.
Thanks for your help!
As always, check earths and wiring methodically and carefully. a good test meter is a must.
Typically there is a relay somewhere in the circuit, so could be several places where a dodgy connection or earth return could be....you should be able to hear a relay 'tick' when pushing horn button, that's probably the place to start, and then as horns work fine off the car, I agree a dodgy earth return is highly likely...
With a test meter, you can see if the supply voltage varies, or the case voltage of the horns goes up, which confirms faulty earth (one end of test meter on battery, other on horn or supply wire)
Typically there is a relay somewhere in the circuit, so could be several places where a dodgy connection or earth return could be....you should be able to hear a relay 'tick' when pushing horn button, that's probably the place to start, and then as horns work fine off the car, I agree a dodgy earth return is highly likely...
With a test meter, you can see if the supply voltage varies, or the case voltage of the horns goes up, which confirms faulty earth (one end of test meter on battery, other on horn or supply wire)
Hi John,
The horn fuse is in the main box, and as this is ran off the purple (permanently live) on the same system as the interior lights and cigar lighter these should be checked to be working 1st.
So, check that these are working..then check the permanent live to the horns (again purple)...once the you have live AT the horns... the horn press earth out is Purple/black..check continuity between the horns and the horn press slip ring wiring connection above your knee (dis-connect this and earth the wire from the horns out as a test).
At this point the earthing the cable out should sound the horns...
On the 3000M (ONLY) both UJ's bolts should have a earth link wire across AND the rack should be earthed to the chassis via the rack nipple (or blank) and the rack U clamp.
Re connect the slip ring wire
Then the horn press slip ring system needs checking...BUT
Do the above simple things 1st...and run that past me.
As,IF the horn press now works and does not sound as your driving them the relationship between the steering wheel/crash clamp and chassis intermediate shaft bronze bush is correct, IF NOT then this will need setting correctly.
Adrian@
The horn fuse is in the main box, and as this is ran off the purple (permanently live) on the same system as the interior lights and cigar lighter these should be checked to be working 1st.
So, check that these are working..then check the permanent live to the horns (again purple)...once the you have live AT the horns... the horn press earth out is Purple/black..check continuity between the horns and the horn press slip ring wiring connection above your knee (dis-connect this and earth the wire from the horns out as a test).
At this point the earthing the cable out should sound the horns...
On the 3000M (ONLY) both UJ's bolts should have a earth link wire across AND the rack should be earthed to the chassis via the rack nipple (or blank) and the rack U clamp.
Re connect the slip ring wire
Then the horn press slip ring system needs checking...BUT
Do the above simple things 1st...and run that past me.
As,IF the horn press now works and does not sound as your driving them the relationship between the steering wheel/crash clamp and chassis intermediate shaft bronze bush is correct, IF NOT then this will need setting correctly.
Adrian@
OK, I did some checking on the car and reviewed my files. I have a wiring diagram .pdf that references my car VIN number 3668TM. Since it doesn't appear I can attach a file here, Adrian, I will email you a copy. I have also updloaded a copy to the Yahoo Pre1980 Group Files for others who may be interested.
EDIT: I uploaded a .jpg view of the wiring diagram to this post. It provides a decent overview but the .pdf version can be zoomed and is more useful. Click the image displayed by thumbsnap for a larger view.
This diagram shows the horn, interior light and my car's cooling fans on one circuit, with the cigar lighter and the hazard flashers on another, contrary to what the owners manual states. My cigar lighter works. My horn and my interior light do not (bulb checks OK) so I suspect my diagram is correct. Not sure if the fans work at the moment but they have worked. I am preparing the car for its first start since the carb rebuild and can't test them yet. The diagram shows a junction where the fans are one direction and the horns and interior light are the other direction. Maybe this is where the problem is. I don't know where this location is physically, however.
Below are two views of my fuse box and photos of the horn and boss. Do you notice anything unusual? I can't match the wires coming from the fuse box to the diagram. There are many more than the diagram shows.
I find no power at the boss or at the horns. At the horns, I found the very light purple wire connectors to be broken so replaced them both. The seller said the horn didn't work and would have it fixed. It worked (weakly) when the car was delivered. You can see some new connectors have been added at the fuse box and in the boss.
Can you please confirm the hot (live) wire at the horns is the solid color light purple and the earth is the brown/green? Does the horn button just complete the earth? No power running through the wire in the boss?
My next move is to simply follow the wiring from the horns and see where it goes. Any advice is appreciated.
EDIT: I uploaded a .jpg view of the wiring diagram to this post. It provides a decent overview but the .pdf version can be zoomed and is more useful. Click the image displayed by thumbsnap for a larger view.
This diagram shows the horn, interior light and my car's cooling fans on one circuit, with the cigar lighter and the hazard flashers on another, contrary to what the owners manual states. My cigar lighter works. My horn and my interior light do not (bulb checks OK) so I suspect my diagram is correct. Not sure if the fans work at the moment but they have worked. I am preparing the car for its first start since the carb rebuild and can't test them yet. The diagram shows a junction where the fans are one direction and the horns and interior light are the other direction. Maybe this is where the problem is. I don't know where this location is physically, however.
Below are two views of my fuse box and photos of the horn and boss. Do you notice anything unusual? I can't match the wires coming from the fuse box to the diagram. There are many more than the diagram shows.
I find no power at the boss or at the horns. At the horns, I found the very light purple wire connectors to be broken so replaced them both. The seller said the horn didn't work and would have it fixed. It worked (weakly) when the car was delivered. You can see some new connectors have been added at the fuse box and in the boss.
Can you please confirm the hot (live) wire at the horns is the solid color light purple and the earth is the brown/green? Does the horn button just complete the earth? No power running through the wire in the boss?
My next move is to simply follow the wiring from the horns and see where it goes. Any advice is appreciated.
Edited by jastx on Thursday 4th October 02:42
I can confirm that the horns (as you say hot) and the horn press is earth out...
IMHO you need to go to the slip ring wire above your knees (as this WILL be correct from the horn press towards back towards the loom and WILL be purple/black) and see what colour is connected to this and trace that back through to both horns. The whole column is the earth..SO the red sprung wire in the steering wheel slides against the slip ring and then with the horn press earth's out through the column (which is why you need each UJ linked across the bolt and the rack to chassis earthed).
Adrian@
IMHO you need to go to the slip ring wire above your knees (as this WILL be correct from the horn press towards back towards the loom and WILL be purple/black) and see what colour is connected to this and trace that back through to both horns. The whole column is the earth..SO the red sprung wire in the steering wheel slides against the slip ring and then with the horn press earth's out through the column (which is why you need each UJ linked across the bolt and the rack to chassis earthed).
Adrian@
Adrian, thank you for the information. I tried another test this morning. I disconnected the live wire and earth from the horn and connected a wire to it directly from the battery (+) and tested touching another lead to earth on the chassis. It worked as expected. I reconnected the earth wire to the horn, intending to then check the horn circuit from the horn button. When I got back to my interior, I found the interior lit as I opened the door and worked normally. When I tested the horn, it made a slight sound but no beep and the interior light dimmed.
I would say I have a short or, more likely, the previous work done on the horn swithed the ground and live wire connections somewhere. Time to follow the wiring, would you agree? Is there a likely place where reversing plug connections could have occurred?
I would say I have a short or, more likely, the previous work done on the horn swithed the ground and live wire connections somewhere. Time to follow the wiring, would you agree? Is there a likely place where reversing plug connections could have occurred?
Edited by jastx on Thursday 4th October 16:00
Fixed it. I got many unexpected continuity readings and my fuse box connections looked nothing like the diagram I had. I compared it to the one in the back of the owners manual. Neither are correct. I was lost, but I went back to the footwell and was able to dig an inline fuse from behind my console with a blown 35A fuse. Replaced that, problem solved.
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