Horn wiring

[sotal]

My horn still isn't working, but I have a bit of time to investigate today.

So I have taken off the offside headlight to give me more access.

So far I have found the relay concerned which clicks nicely when the horn is pressed (it looks very clean with nor visible corrosion etc.)

I have also disconnected the horn on that side and connected 12v straight from the battery which sounds the horn. If I connect the unconnected wire to 12v then the other horn sounds proving that the link between the 2 horns is good.

Testing the relay I got unexpected results.

Using the wiring diagram codes from: http://www.g8dhe.net/bwm/bwmanualp.htm?1999/Page_76

Without the horn being pressed I get:

Y/R(F) C = 12v
Y/R(F) A = 12v
G/R (F) = 0v
G/O (F) = 12v

When the horn is pressed I get:

Y/R(F) C = 0v
Y/R(F) A = 12v
G/R (F) = 0v
G/O (F) = 1.6v

I've generalised with the 12v reading - it was approx 12.6v


From the wiring diagram, the Y/R wires both look to be connected together so I can't see how it can be possible for one to be at 12v and the other at 0v???

I have tried swapping the relay for the neighbouring relays with no change (what are the next two relays for?)

I've checked the fuse which was perfect.

Any suggestions as to where to look next?

I'm going to continue to have a look at it but I expected it to be a break on the G/R wire between the relay and the point where it splits off in two directions. The relay readings have made me unsure of that now but will focus on that being the most likely.

[sotal]

I'm a little bit further.

To test the G/R wire further, I removed the relay and applied 12v to connector that is connected to the G/R wire - both horns sounded.

This gave me the conclusion that the wire from the horn switch to the relay works and the wire from the relay to the horns themselves works too.

That only left the 12v supply and the relay (but I'd tried other relays in its place). I couldn't get my head round how the 2 Y/R wires are supposed to be connected together yet they both show 12v before the horn is pressed but only the one shows 12v after the horn is pressed.

To test further I made some cables up to connect the relay separately. So I could test it easier and connect directly (via an inline fuse to the battery)

I started by connecting the G/R and G/O directly to the relay and applying 12v to both the Y/R wires from the battery. The horn now worked perfectly when the button is pressed. I now tried connecting them both to one of the normal relay wires (the one marked A on the diagram) - it still worked, however when connected to the one marked C on the diagram it stopped working. Connecting them separately to A and C resulted in it no longer working too.

So it appears that there is something wrong with the wire connecting to the connection marked 'C'. I've no idea how far back they go before they split apart from the same source, but I take it I can just cut it behind the relay and join it to 'A' at that point?

That would still match the wiring diagram.

[sotal]

Continued testing- found that the Y/R wire which had 12v but then went to 0v when the horn was pressed was unable to support any load. The test light would not light.

I went with my idea above. I took out the two terminals from the relay connection. Cut the duff wire wire a couple of inches down and looped it back to the other connector. Then pushed the terminals back into the connector.

It follows the wiring diagram and works perfectly, the only downside I can think of is that I don't like the idea that it is possibly a break which was stopping it from working and that break is still there with a potentially live side to it.

[g8dhe]

Its not totally unknown for vibration to cause a break of the wire within the insulation and then corrosion sets in and provides a high resistance electrical path so a digital voltmeter says 12v but then as soon as the load appears virtually nothing.

[bongojoe]

I had exactly the same problem as described above—horn not sounding, fuse tested okay, relay clicking happily and tested okay, but 12v getting to relay on only one of the two yellow / red wires.

I figured—also based on wiring diagram—that connecting the two yellow / red wires at the relay would solve the problem but worried a single wire wouldn't be designed to carry the current for both activating relay and sounding the horn. However at the fusebox end it's exactly the same gauge, so can't see any issues.

Horn working fine now. Parp parp!

[sotal]

Mine has worked ever since, I've seen a few have the same problem now so I think it is becoming a common problem. It isn't too hard to fix though. Maybe it needs to become a guide for the members area?

[bongojoe]

Sounds like a good idea. Not sure I could bear the responsibility of being its author, but I'm happy to edit if you want to write!

[BongoRaceTruck]

That was the problem with mine, if only I'd spend a bit more time on here than trying to fault find myself!!!

Thanks Guys

Matt