Horn problem

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Balmain Bill

Balmain Bill

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Just getting my Mk3 back together after a rear isolastic replacement and a new wiring loom/assimilator and noticed that the horn wasn't working, giving only that faint hollow 'pop' that would normally indicate a flat battery. However the battery was fully charged so I figured it might be the contacts needed adjusting.

So I pulled the horn out (there's fun) stuck it on the bench and tested it and it was fine. Reinstalled it cleaning off all the surfaces, nipped it up nice and tight, tried it again and I'm back to the 'popping'. I've checked the wiring and that seems fine, I was careful to install the assimilator correctly (thanks to all of the posts on this forum - thanks guys).

I also note that I have no main/dip beam on the headlight (bulb is OK) and I'm starting to wonder if they are related operating from the same switch assembly. I haven't had the switch apart yet but thought I might see if anyone had any clues.
 
Balmain Bill said:
Reinstalled it cleaning off all the surfaces, nipped it up nice and tight, tried it again and I'm back to the 'popping'. I've checked the wiring and that seems fine, I was careful to install the assimilator correctly (thanks to all of the posts on this forum - thanks guys).
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If you are sure the wiring, including the ground/return (red) is as it should be, then I would suspect the horn button switch contacts could be the cause. The only way I could get my Mk3's horn to work properly even after cleaning the switch contacts was to fit a relay.



Balmain Bill said:
I also note that I have no main/dip beam on the headlight (bulb is OK) and I'm starting to wonder if they are related operating from the same switch assembly. I haven't had the switch apart yet but thought I might see if anyone had any clues.
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Only the headlamp flasher switch is powered from the same feed as the horn switch (white 'W').

The standard headlamp main/dip feed is blue/yellow 'UY' from ignition switch terminal 4 to the HEAD - PILOT switch on the RH cluster, then blue 'U' between the head - pilot switch and the LH switch cluster, so check power is reaching the LH cluster from the 'Head-Pilot' when set at the 'Head' position.
 
If you can, measure the voltage from the battery to the horn on both the earth wire and the negative lead (if it's positive ground). If you have any amount of voltage on either line when trying to operate the horn, the problem is in the lead with the voltage. But you will still have to find where the resistance (voltage drop) is. It may get you to the area or at least to the suspect wire.
 
L.A.B. said:
If you are sure the wiring, including the ground/return (red) is as it should be, then I would suspect the horn button switch contacts could be the cause. The only way I could get my Mk3's horn to work properly even after cleaning the switch contacts was to fit a relay.
Click to expand...


LAB, can I ask what relay you fitted and how you wired it up?
 
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Balmain Bill said:
Just getting my Mk3 back together after a rear isolastic replacement and a new wiring loom/assimilator and noticed that the horn wasn't working, giving only that faint hollow 'pop' that would normally indicate a flat battery. However the battery was fully charged so I figured it might be the contacts needed adjusting.

So I pulled the horn out (there's fun) stuck it on the bench and tested it and it was fine. Reinstalled it cleaning off all the surfaces, nipped it up nice and tight, tried it again and I'm back to the 'popping'. I've checked the wiring and that seems fine, I was careful to install the assimilator correctly (thanks to all of the posts on this forum - thanks guys).

I also note that I have no main/dip beam on the headlight (bulb is OK) and I'm starting to wonder if they are related operating from the same switch assembly. I haven't had the switch apart yet but thought I might see if anyone had any clues.
Click to expand...

Also note that the horn itself must be free to vibrate or else little or no noise will be emited.
If any part of the horn except its mounting spring plate is touching anything else that will be a problem.
Even after you figure it out the feeble horn will leave you dissapointed.
Ride On (honking)
Dave
 
crusadersports said:
LAB, can I ask what relay you fitted and how you wired it up?
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A standard 4-pin 30,85,86,87 relay in the battery compartment. The harness horn wires (PB and R) connect to the relay and a short made-up section connects the horn to the relay.Edit: And a brown/blue 'NU' power feed.
Horn problem
 
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Thanks LAB. The horn on my mk 3 has been woeful for years.Good enough at rest and still passes the MOT, but useless on the move. Never thought of checking the horn button...!
 
Thanks @L.A.B. @The Buckeye Rider and @DogT for your suggestions. I am now working my way through the various points you made, first up whether the horn was touching anything which it was, being in contact with both of the oil feeds. They took some jiggling but they're clear now. Tried changing the position of the horn so that it points to the other side and whilst it was clear of the swing arm and the chain guard it was pointing upwards of course and would fill with rain water, so that isn't an option. I see there's few threads on horn position but I wanted to try revising it for myself.

Unfortunately the horn touching the oil pipes wasn't the problem so I'm now in the process of adding an additional (temporary) earth to confirm/eliminate the dodgy earth theory. Next up is the switch gear - the headlight bulb is intact but there's a jumble of wires and insulating tape in there that look a bit like the spag bol I had for dinner last night so that will be interesting. I'll keep you posted - thanks again.
 
Balmain Bill said:
Next up is the switch gear - the headlight bulb is intact but there's a jumble of wires and insulating tape in there that look a bit like the spag bol I had for dinner last night so that will be interesting.
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Balmain Bill said:
Just getting my Mk3 back together after a rear isolastic replacement and a new wiring loom/assimilator
Click to expand...

Maybe finish the wiring loom job? ;):)

https://andover-norton.co.uk/en/shop-details/20590/headlamp-harness-850mk3-pvc
 
So - grabbed the voltmeter (as suggested, thanks @concours) and the live terminal on the horn was receiving just 0.5 volts when the horn was operated. Checked the voltage from the battery to the terminals on the horn as suggested (thanks @DogT) and on operation the earth showed zero and the live 12.5 volts. So I followed the lead back to the horn button and there were no shorts, all good. Checked that power was getting to the LH cluster (thanks @L.A.B.) - all good. I don't have a pilot switch however, both switch clusters have been replaced and the indicators have been removed which explains the mess in the headlight shell.

Pulled the LH switch gear apart and gave it a tidy up even though it is quite new. Still nothing but that hollow 'flat battery' pop. So I went back to the horn and turned the tone adjuster a quarter turn and bingo, I was greeted with that sad half arsed Norton moan that after a day of messing around I've gotta say sounded pretty damn good. But I can't explain or understand how the live terminal was only getting 0.5 volts when I tested out earlier in the day.

So - headlight tomorrow. Hopefully something equally simple.
 
That doesn't sound so simple if you really didn't find anything other than now it works. The thing is you can measure 0 ohms when the circuit is dead, ie. no current. But when you introduce current into the line, all of a sudden you have a large increase in resistance at some point. I've seen it more than once. The only way to measure that is to measure voltages along the line from point to point (connection to connection) with the horn button pushed. You may have the problem again later. Or perhaps it was just the tone adjuster.
 
Balmain Bill said:
But I can't explain or understand how the live terminal was only getting 0.5 volts when I tested out earlier in the day.
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To get a reading of 0.5V I suspect what you were probably measuring was voltage drop.
 
Funny that it worked fine on the bench without turning the tone adjuster... Is there a bullet connection under the tank with your setup from the horn to the button? That isn't loose it is?
 
Supercat said:
Funny that it worked fine on the bench without turning the tone adjuster... Is there a bullet connection under the tank with your setup from the horn to the button? That isn't loose it is?
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Yes that is a bit odd, I forgot about that. When it was on the bench it was loud and clear too but it was straight off the battery which suggests that it's losing some voltage on the way through and that the direct connection was enough to give what were possibly gummy contacts a sufficient kick in the guts to burst into life.

How often do these horns need adjusting? Hopefully twice a century given the location.

The connection under the tank is the standard white cluster but I'm questioning the rest of the wiring now having only replaced the main harness which was probably false economy in hindsight. I'll replace it all anyway now.
 
That .5V voltage drop LAB is talking about may be enough just for the horn not to work where in the bench, you probably don't have that .5V drop with short leads and no bad (maybe) connectors.

I had this problem with my tractor not starting recently and I thought I needed new batteries, but I did a few tests and found that there was one of those aftermarket battery connectors with a large lead to the starter and although I could measure 12V at the starter, when I tried starting I only got maybe 3 V at the starter under load (during starting). There was a huge voltage drop in that old connector. Cleaned it up and now it starts and I didn't need to buy 2 $120 batteries for this diesel tractor. That connector didn't show up with resistance checks either, but put 50Amps through it and boy did it show up.
 
DogT said:
That .5V voltage drop LAB is talking about may be enough just for the horn not to work where in the bench, you probably don't have that .5V drop with short leads and no bad (maybe) connectors.

I had this problem with my tractor not starting recently and I thought I needed new batteries, but I did a few tests and found that there was one of those aftermarket battery connectors with a large lead to the starter and although I could measure 12V at the starter, when I tried starting I only got maybe 3 V at the starter under load (during starting). There was a huge voltage drop in that old connector. Cleaned it up and now it starts and I didn't need to buy 2 $120 batteries for this diesel tractor. That connector didn't show up with resistance checks either, but put 50Amps through it and boy did it show up.
Click to expand...
When you say 'after market battery connector' do you mean the connector that fixes to the battery terminal itself?
 
L.A.B. said:
A standard 4-pin 30,85,86,87 relay in the battery compartment. The harness horn wires (PB and R) connect to the relay and a short made-up section connects the horn to the relay.Edit: And a brown/blue 'NU' power feed.
Horn problem
Click to expand...
Pardon my ignorance on this @L.A.B. ('lectrix not being my strong suit 'n' all) but what is the purpose of the relay? and what does it actually do?
 
DogT said:
I had this problem with my tractor not starting recently and I thought I needed new batteries, but I did a few tests and found that there was one of those aftermarket battery connectors with a large lead to the starter and although I could measure 12V at the starter, when I tried starting I only got maybe 3 V at the starter under load (during starting). There was a huge voltage drop in that old connector. Cleaned it up and now it starts and I didn't need to buy 2 $120 batteries for this diesel tractor. That connector didn't show up with resistance checks either, but put 50Amps through it and boy did it show up.
Click to expand...

I had the same problem a couple months ago on my JD. Got the old battery terminal wire brush out and gave the terminals and connectors a good scrub, and bam, fired right up.
 
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