Where is the horn relay?

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mvg

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On a 2005 LR3 HSE, the electrical reference states that it is an integral part of the central junction box (CJB). I only see three relays attached to the it and none of them is for the horn.

Horn went on continuously while driving and only stopped when fuse burned out. Replacing fuse just burns itself out. Wire circuitry from horn switch to CJB indicates no short circuit. However, from horn to CJB does. Disconnecting at CJB the connector leading to the horn removes the short circuit condition. This tells me short is in the CJB. Replacing it sounds costly. Less costly alternative is to bypass with new relay circuitry, but alarm will not have a horn to use.
 

ryan-in-oregon

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Disconnecting at the cjb tells me it is in the wiring not the cjb. Maybe the horn itself is shorted. With the wires lose at the cjb check for resistance to ground if any you have found the shorted wire now you just need to find the break.
 

mvg

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Ryan, thanks for your help. I had disconnected the connector at the horn and measured the resistance. Short. I then disconnected the connector at the CJB and measured the resistance again at the horn connector. No short. I concluded then that the wire from horn connector to CJB connecter is OK. Short then is in CJB, most likely the horn relay. But I can't find the relay.
 

RobertColunga

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Hi mvg! I'm also having this same issue and I also cant find this relay as well... i can't find my car parts manual to track the position of this thing... did you able to find it?
 

bbyer

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maybe the clockspring

Below is the link to the horn wiring circuit.

It is possible that there is a problem with the circuit board internally mounted relay, ( FET, Field Effect Transistor, I believe they are called), but per the wiring diagram, I note that the clockspring located within the steering wheel hub is also a part of the horn circuit.
The clockspring has been a troublesome part in the early 3's and was subject to a replacement instruction early on.

The FET's serve the same purpose as a relay but are micro miniature things within the circuit board. I discovered this when I went looking for the power window relays - took me a couple of months of searching to figure out that they were not ********* lumps hiding somewhere.

Also I would run power to each of the two horns separately just to prove that each works as it should. Often with the 3, a problem is something simple but finding it is not.

http://www.disco3.co.uk/gallery/albums/userpics/15405/LR3_Horn_Wiring_p_74.pdf
 

bbyer

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maybe the clockspring

Below is the link to the horn wiring circuit.

It is possible that there is a problem with the circuit board internally mounted relay, ( FET, Field Effect Transistor, I believe they are called), but per the wiring diagram, I note that the clockspring located within the steering wheel hub is also a part of the horn circuit.
The clockspring has been a troublesome part in the early 3's and was subject to a replacement instruction early on.

The FET's serve the same purpose as a relay but are micro miniature things within the circuit board. I discovered this when I went looking for the power window relays - took me a couple of months of searching to figure out that they were not ********* lumps hiding somewhere.

Also I would run power to each of the two horns separately just to prove that each works as it should. Often with the 3, a problem is something simple but finding it is not.

http://www.disco3.co.uk/gallery/albums/userpics/15405/LR3_Horn_Wiring_p_74.pdf
 

bbyer

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FET not a relay like in the LR wiring diagrams

It occurred to me that while the FET's act like relays, from the view of a conventional ohmmeter, they do not test out that way.

The link below is to a number of FET relay designs, none of which look to a conventional ohmmeter like a magnetic coil and a set of contacts. Hence to a conventional ohmmeter, I think the FET will probably look like a short circuit.

A possible test would be to try the ohmmeter across a FET relay that seems to be working. One reason for the FET's is that they provide current monitoring in addition to the relay function and hence send trouble info off to the monitoring systems. In a perfect world, they are sometimes supposed to open before a fuse goes. This is in part how the auto power window reverse function works - when the current draw is some amount higher than previous times, the window reverses direction.

http://www.google.ca/search?q=fet+r...FLu_ZiAL87vGxAg&ved=0CEcQsAQ&biw=1280&bih=886
 

mvg

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Follow-up to horn short: My assumption that the short was in the CJB is wrong. I found another horn (low tone) behind the left headlight, which was the one that was shorted. The high-tone horn is located behind the front grille. I had thought that the North American version had only one horn, because that is all I could initially find ignoring what the circuit diagram indicated. These two horns are connected electrically within the CJB so that when I disconnected the wire from the horn in the grille and measured the resistance at the disconnected CJB connector, the short went away making me conclude erroneously that the short is not in the wire, but in the CJB. The only reason the short went went away is because I disconnected the CJB connector. Reconnecting the CJB connector reconnected the shorted horn behind the headlight with the one in the grille and because I assumed there was only one horn, I concluded erroneously that the short is in the CJB.

Findings: the horn relay is built into the CJB. Fortunately, the horn fuse blows before damage is done to the CJB.

My Fix: Replace the shorted horn behind the headlight.

This was in March. About three months later, June, the same thing happens, but this time it's the horn inside the grille. I disconnect the grille horn with plans to replace it when I had the time. However, a month later, July, the same thing happens again to the horn behind the headlight, the one I just replaced in March. I'm wondering if this is a bad batch of horns. Brand is Fiamm. I need to buy a new set of horns and can't believe how problematic these horns are.
 

bbyer

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3 defective horns?

This is sounding odd. I suppose that when a ground occurs for whatever reason, what you are hearing is the "good" horn and it blows until either disconnected, burns out, or the fuse blows. It then appears to be the "bad" horn.

In your case, the fuse eventually blew in I suppose both cases. To my knowledge, horns are not designed for continuous use, (well Italian ones like Fiamm should be), so maybe the failure of the subsequent horns was a result of the first grounding event.

Under the circumstances, if I installed a new horn, I would disconnect the other horn for at least a month to sort of test the circuit re the new horn. If OK, then I would disconnect that first horn and connect up the second one, again for another month or so before running both horns together.

The real question is where is the grounding action occurring that initiates a flow of power to cause the "good" horn to sound and then burn out. In other words, the horn that burned out was not the cause and hence was not the defective horn; it is perhaps the "other" one, and since the problem is intermittent, the "bad" horn appears to be OK.

If both horns were blowing, it could still be that the good one burned out first as the defective one may not have been sounding full out. Also since it was some time before you discovered the second horn, well .... Land Rovers are rarely easy to figure out.
 

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