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Ray White
Joined: 02 Dec 2014
Posts: 6310
Location: Derby
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 Posted: Tue Jan 19, 2021 11:58 pm Post subject: |
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DM. That diagram is very helpful. I hope I can follow it correctly.
You are most kind to help me understand what has always been a mystery to me.
The only problem is that A3 is not live. Because the normally closed contact on the left coil was not closed I thought I had better disconnect the coils altogether. I de soldered them from their vertical stakes and linked the stakes together with a thick wire.
I presume it will be O.K. to take a link from A1 to A3? |
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DM
Joined: 21 Dec 2008
Posts: 212
Location: North Cornwall
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| Posted: Wed Jan 20, 2021 8:48 am Post subject: |
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A3 will not be live, it is also switched by the ignition relay so the accessories only work with the ignition on which is how it worked when new.
If you link from A1 to A3 you will bypass the ignition switch and the relay so the coil and accesories will be permanentley live. |
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Ray White
Joined: 02 Dec 2014
Posts: 6310
Location: Derby
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| Posted: Wed Jan 20, 2021 9:40 am Post subject: |
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| DM wrote: | A3 will not be live, it is also switched by the ignition relay so the accessories only work with the ignition on which is how it worked when new.
If you link from A1 to A3 you will bypass the ignition switch and the relay so the coil and accesories will be permanentley live. |
O.K. That makes sense. Thanks again.
Have a safe day. |
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Ray White
Joined: 02 Dec 2014
Posts: 6310
Location: Derby
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| Posted: Wed Jan 20, 2021 5:41 pm Post subject: |
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As the alternator and ignition switch relays are sited next to each other I have taken the opportunity of combining their ground wires as a matter of neatness and economy.
Is there any reason why the wire from terminal 85 from one relay should not be linked to T85 from the other in a similar fashion? |
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DM
Joined: 21 Dec 2008
Posts: 212
Location: North Cornwall
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| Posted: Wed Jan 20, 2021 7:04 pm Post subject: |
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| Ray White wrote: | As the alternator and ignition switch relays are sited next to each other I have taken the opportunity of combining their ground wires as a matter of neatness and economy.
Is there any reason why the wire from terminal 85 from one relay should not be linked to T85 from the other in a similar fashion? |
You can link T85 from both relays together and feed them with 1 wire from the ignition switch, would make a tidier installation. |
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Ray White
Joined: 02 Dec 2014
Posts: 6310
Location: Derby
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| Posted: Wed Jan 20, 2021 7:43 pm Post subject: |
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| DM wrote: | | Ray White wrote: | As the alternator and ignition switch relays are sited next to each other I have taken the opportunity of combining their ground wires as a matter of neatness and economy.
Is there any reason why the wire from terminal 85 from one relay should not be linked to T85 from the other in a similar fashion? |
You can link T85 from both relays together and feed them with 1 wire from the ignition switch, would make a tidier installation. |
Excellent! That is just what I want to achieve.  |
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Ray White
Joined: 02 Dec 2014
Posts: 6310
Location: Derby
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| Posted: Wed Jan 20, 2021 9:19 pm Post subject: |
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So do these two relays do more than protect the alternator and ignition switch?
I am particularly keen on protecting the electronic distributor. Will it require a separate relay? |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4104
Location: South Cheshire
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| Posted: Wed Jan 20, 2021 9:38 pm Post subject: |
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| Ray White wrote: | So do these two relays do more than protect the alternator and ignition switch?
I am particularly keen on protecting the electronic distributor. Will it require a separate relay? |
Ray , a relay won't protect the alternator or electronic distributor, it simply moves the load from a switch to the relay, so only "protects" switch contacts.
Dave |
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Ray White
Joined: 02 Dec 2014
Posts: 6310
Location: Derby
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| Posted: Wed Jan 20, 2021 10:22 pm Post subject: |
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| ukdave2002 wrote: | | Ray White wrote: | So do these two relays do more than protect the alternator and ignition switch?
I am particularly keen on protecting the electronic distributor. Will it require a separate relay? |
Ray , a relay won't protect the alternator or electronic distributor, it simply moves the load from a switch to the relay, so only "protects" switch contacts.
Dave |
What I understood was that the diode in the relay prevented stray high voltage spikes from damaging electronics.? |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4104
Location: South Cheshire
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| Posted: Wed Jan 20, 2021 10:27 pm Post subject: |
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| Ray White wrote: | | ukdave2002 wrote: | | Ray White wrote: | So do these two relays do more than protect the alternator and ignition switch?
I am particularly keen on protecting the electronic distributor. Will it require a separate relay? |
Ray , a relay won't protect the alternator or electronic distributor, it simply moves the load from a switch to the relay, so only "protects" switch contacts.
Dave |
What I understood was that the diode in the relay prevented stray high voltage spikes from damaging electronics.? |
Its the relay coil itself that generates the high voltages (back EMF) , hence the precaution in fitting a diode across the coil.
Dave |
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Ray White
Joined: 02 Dec 2014
Posts: 6310
Location: Derby
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| Posted: Wed Jan 20, 2021 10:40 pm Post subject: |
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I am still on a steep learning curve!
I will presumably need a relay if I am to protect the ancient horn button.? The same switch incorporates a headlamp dip switch. Will it be the horn or the headlamp relay that protects the dipping function? |
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MVPeters
Joined: 28 Aug 2008
Posts: 822
Location: Northern MA, USA
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| Posted: Wed Jan 20, 2021 11:19 pm Post subject: |
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Ray
I'm no electrician, but just for clarity, a relay is little more than a remote switch to carry a heavy current, triggered by a switch designed for a light current.
In early cars, a relay is often used for the horn, occasionally the headlights & little else.
Introducing a relay into a circuit that doesn't really need it adds another point-of-failure. An arbitrary value might be 5 amps; any device that consumes less is adequately handled by a dashboard switch, anything more might be a candidate for a relay.
Personally, I would not add a relay to a critical ignition circuit.
_________________
Mike - MVPeters at comcast.net
2002 MINI Cooper 'S' |
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Ray White
Joined: 02 Dec 2014
Posts: 6310
Location: Derby
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| Posted: Thu Jan 21, 2021 12:28 am Post subject: |
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| MVPeters wrote: | Ray
I'm no electrician, but just for clarity, a relay is little more than a remote switch to carry a heavy current, triggered by a switch designed for a light current.
In early cars, a relay is often used for the horn, occasionally the headlights & little else.
Introducing a relay into a circuit that doesn't really need it adds another point-of-failure. An arbitrary value might be 5 amps; any device that consumes less is adequately handled by a dashboard switch, anything more might be a candidate for a relay.
Personally, I would not add a relay to a critical ignition circuit. |
I too would like to avoid failure if possible. I have been advised to protect the ignition/lighting switch with a relay from someone who had four of them fail before doing so. The horn/dip switch is also vulnerable... |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4104
Location: South Cheshire
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| Posted: Thu Jan 21, 2021 11:27 am Post subject: |
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| Ray White wrote: | | MVPeters wrote: | Ray
I'm no electrician, but just for clarity, a relay is little more than a remote switch to carry a heavy current, triggered by a switch designed for a light current.
In early cars, a relay is often used for the horn, occasionally the headlights & little else.
Introducing a relay into a circuit that doesn't really need it adds another point-of-failure. An arbitrary value might be 5 amps; any device that consumes less is adequately handled by a dashboard switch, anything more might be a candidate for a relay.
Personally, I would not add a relay to a critical ignition circuit. |
I too would like to avoid failure if possible. I have been advised to protect the ignition/lighting switch with a relay from someone who had four of them fail before doing so. The horn/dip switch is also vulnerable... |
Ray I presume you have the Lucas PLC combined ignition/charge/light switch? They tend to get warm with the headlights on full beam, and if the contacts are worn get hot hence the fire risk. So worth adding a relay to the headlamp circuit but not for anything else related to the switch. Horns don't usually present a fire risk as the are only used momentarily, however they do draw a relatively large current that will wear the contacts, so adding a relay will increase reliability.
When I was a know it all youth  I bought a Bedford CA for £60, it really needed new dampers and track rod ends, but instead I decided it require a set of air horns! The air horn set came with a relay, but in my youthful arrogance I thought this was unnecessary complication so simply wired them into the existing horn wiring. The high current required to get the air horn spinning was clearly to much for the van horn switch, which resulted in the compressor taking a couple of seconds to get up to speed, resulting is a gurgling's /squawking sound until the full blast was achived!
Dave
Last edited by ukdave2002 on Thu Jan 21, 2021 11:59 am; edited 1 time in total |
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Ray White
Joined: 02 Dec 2014
Posts: 6310
Location: Derby
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| Posted: Thu Jan 21, 2021 11:58 am Post subject: |
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No Dave. I do not have that switch. The one I have is a Lucas PRS3 not normally found on MG. (See my dashboard thread). I shall not be changing it for a PLC with this instrument cluster.
(I have a PLC switch on an 'original' design dashboard that will not be fitted). |
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