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Ray White
Joined: 02 Dec 2014 Posts: 6349 Location: Derby
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Posted: Tue Mar 01, 2022 5:50 pm Post subject: Horn button ground? |
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Hello everyone. This horn button, combined with a main beam dip switch, is normally (on a standard T Type MG) mounted on the metal instrument panel. On my car it is to be mounted onto the wooden dashboard and I think I may have an issue with regard to earthing. I have taken some photos to give an idea of how I think it should work.
I am assuming the feed to the horn button should be soldered to the middle of the insulated disc?
When the button is depressed against the spring pressure a connection is made with the case and should (I think) be earthed through the two brass machine screws that would normally be attached to the metal instrument panel?
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The question I have is how should I organise an accessible earth wire from the horn button given the fact that the machine screws don't go all the way through the wood.? I don't know how readily available some longer 4 BA screws might be.
I am making assumptions about how I think the horn works as I have not any original fittings or wires to copy. I am quite prepared to accept that I may be wrong and I am open to suggestions but I do need to keep the wiring behind the dash. |
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ukdave2002
Joined: 23 Nov 2007 Posts: 4122 Location: South Cheshire
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Posted: Tue Mar 01, 2022 6:17 pm Post subject: |
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Counter bore enough to fit a nut and terminal? |
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Ray White
Joined: 02 Dec 2014 Posts: 6349 Location: Derby
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Posted: Tue Mar 01, 2022 7:58 pm Post subject: |
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ukdave2002 wrote: | Counter bore enough to fit a nut and terminal? |
The difficulty is that I would need to counter bore from behind the dash and in the corner of the frame.
I don't think I can do it. I can't see what I am doing.
I am toying with the idea of soldering earth wires onto the ends of the brass machine screws in a way that still allows them to thread through the captive nuts.
Ideally I would fit longer machine screws but I have not yet been able to find any.
I am tempted to make some from studding...
https://www.ebay.co.uk/itm/330708580668?var=540059344639&ssPageName=STRK%3AMEBIDX%3AIT&fromMakeTrack=true |
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Bitumen Boy
Joined: 26 Jan 2012 Posts: 1737 Location: Above the snow line in old Monmouthshire
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Posted: Tue Mar 01, 2022 9:01 pm Post subject: |
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I think longer screws from studding - well, I guess you'd only really need one - would be perfectly acceptable. Or as you say a soldered connection to the end of a shorter screw, though that might be fragile and I think you'd probably want a suitable die to clean up the end of the thread and allow a nut to screw on to it - I assume you'd be wanting to fit the nut over the length of cable after soldering, but I could be wrong there.
Another thought, though, is that it might be worth tracking down and speaking to the folks that make the studding - given the limited demand for anything threaded 4BA these days I'd hazard a guess that the studding you link to is made on a lathe in small quantities, and it may well be quite straightforward for them to produce longer screws as specials. |
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Ray White
Joined: 02 Dec 2014 Posts: 6349 Location: Derby
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Posted: Tue Mar 01, 2022 9:38 pm Post subject: |
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Well, I have ordered a 12" length of 4 BA brass studding.
Fortunately I have a good supply of BA nuts and washers.
I have yet to decide on how best to create a slotted head. In the past I have soldered on a nut and cut a slot with a junior hacksaw. If I want to re create the same head shape it is a fairly easy matter to file the corners off... but it is also easy to mess it up. !
If I am unhappy with my efforts I do know a model engineer who would be able to come to my rescue
Funny how things always seem to happen in the wrong sequence. At least that seems to be my experience! |
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ukdave2002
Joined: 23 Nov 2007 Posts: 4122 Location: South Cheshire
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Posted: Wed Mar 02, 2022 9:12 am Post subject: |
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If all else fails you could use the screws that are used to hold the fronts on electrical sockets.
They are M3.5 so only 0.1mm narrower than 4BA, countersunk slotted head, made of nickel plated brass, so you could polish the nickel from the head if desired, and readily available in various lengths up to 100mm.
Best of all the screws and nuts cost pence
Dave
https://www.screwfix.com/p/easydrive-electrical-screws-m3-5-x-75mm-50-pack/2792h
Last edited by ukdave2002 on Wed Mar 02, 2022 9:20 am; edited 1 time in total |
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Ray White
Joined: 02 Dec 2014 Posts: 6349 Location: Derby
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Posted: Wed Mar 02, 2022 9:18 am Post subject: |
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ukdave2002 wrote: | If all else fails you could use the screws that are used to hold the fronts on electrical sockets.
They are M3.5 so only 0.1mm narrower than 4BA, countersunk slotted head, made of nickel plated brass, so you could polish the nickel from the head if desired, and readily available in various lengths up to 100mm.
Best of all the screws and nuts cost pence
Dave |
Yes! I will try that today.!!
Thanks, Dave! |
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ukdave2002
Joined: 23 Nov 2007 Posts: 4122 Location: South Cheshire
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Posted: Wed Mar 02, 2022 9:32 am Post subject: |
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Ray White wrote: | ukdave2002 wrote: | If all else fails you could use the screws that are used to hold the fronts on electrical sockets.
They are M3.5 so only 0.1mm narrower than 4BA, countersunk slotted head, made of nickel plated brass, so you could polish the nickel from the head if desired, and readily available in various lengths up to 100mm.
Best of all the screws and nuts cost pence
Dave |
Yes! I will try that today.!!
Thanks, Dave! |
If important make sure they are nickel plated brass, most are, but I have seen plain mild steel versions. |
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Ray White
Joined: 02 Dec 2014 Posts: 6349 Location: Derby
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Posted: Wed Mar 02, 2022 10:55 am Post subject: |
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Dratts! I only have one long screw!
Not only that but I have just realised that the original horn button screws are smaller than 4BA. I thought they were the same size as the indicator screws but I suppose they must be 5 BA....??
Not only that but I checked and they are not even brass!
What I am thinking of doing is soldering an earth wire to the underside of the fixed brass middle section (collector ring?); taking it down the same route as the live wire and leaving the original screws in place. I think this will work. |
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MVPeters
Joined: 28 Aug 2008 Posts: 822 Location: Northern MA, USA
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Posted: Thu Mar 03, 2022 2:01 am Post subject: |
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BA threads in 'odd' 1 3 5 7 sizes are rare - try a local hobby shop. _________________ Mike - MVPeters at comcast.net
2002 MINI Cooper 'S' |
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Ray White
Joined: 02 Dec 2014 Posts: 6349 Location: Derby
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Posted: Thu Mar 03, 2022 9:48 am Post subject: |
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MVPeters wrote: | BA threads in 'odd' 1 3 5 7 sizes are rare - try a local hobby shop. |
As I have said, I shall not be using the screws for the earth pathway. They are needed for holding the horn button assembly together so I shall leave it at that.
Yesterday I soldered the feed wire to the horn button and another wire to the other side of the insulation and took Both wires through the back ...along with wires for the dip switch.
I now need to connect feed and return wires to the main beam warning light. Please see my previous post about wire colours. |
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