CORRECT way to wire 6RA Lucas overdrive relay?

[Greta]

the 2007 thread about this leaves me still confused.

I'll not prejudice your suggestions but I believe my relay may be goosed because it might have been incorrectly connected. It no longer clicks when ign on,  in gear and switch activated. - It had been working so previous set up worked but I think the live feeds may have been the wrong way around.


6RA Has 4 Terminals, W1, W2, C1 & C2

There are 4 wires, ( On mine ) ... which I think are?

1) Brown - Constant live 12V higher amp gauge
2) White - connected to coil - 12V Ign feed
3) Yellow - from column O/D Switch
4) Purple - to O/D Solenoid

I want to ensure I wire correctly before I start chasing problems in the Overdrive or solenoid. There are also other almost identical relays some rated 24V - I assume they won't work. Advice as to most reliable source also appreciated as there seem to be several options and I suspect several lucas copies.

Please only post if you are 100% confident - threads elsewhere suggest Haynes may be wrong?

[DaveKent]

W1 and W2 are your control circuit, ie  power and earth, one of which will be switched to complete the operating circuit of the relay coil, C1 and C2 are your load circuit, ie power in and component connection.

[Hogie]

To add colour to Dave's post

C1 - Brown (or Brown/White)   +12V from ammeter/solenoid etc
C2 - Yellow/Purple                    to the solenoid
W1 - White                              +12V from ignition switch
W2 - Yellow (or yellow/green)   to the column switch

C1 & C2 can be interchanged
W1 & W2 can be interchanged

This correct for a TR4A negative earth and works
See this also http://www.advanceautowire.com/tr24a.pdf

Also there are four different 6RA relays - make sure you have the right one.

Roger

[Greta]

Thanks guys - it was wired correctly so I guess the relay really is goosed.

That's the clearest wiring diagram I've ever seen. ( Have you a similarly clear diagram that shows how to convert from Dynamo to Alternator - the clearest online diagram I could find doesn't match the rather garbled instructions posted with my dynastar.


Just for completeness - Can one use the more modern cube type relay - if so what are the equivalent terminals?

[JohnD]

Coming late to this, but to point out that a multimeter and a little understanding of what happens in a relay, will let you work it out.

For relays that have four terminals, two are the coil and two for the feed and supply to the unit to be switched.
Only the first pair are in continuity on the bench, so set your MM to resistance, or "continuity" if you have it (it will bleep if you touch the probes together) and test the terminals.
One pair will show that they are connected - that is the coil and should be wired to the switch on your dashboard or whatever.

The other pair are to be wired to a supply and to the unti to be powered.

Simples!
John

PS circuit diagrams of the Lucas 6RA relays are readily available online.

[TedTaylor]

I have a simple way of remembering especially when after 50 years of doing car electrics my aged brain gives up the ghost momentarily.

Refer to John's useful diagrams above

'W' is Wires in the operating coil.
'C' is the switching Contacts.

MUT

[piman]

Hello John,

are those Lucas relay diagrams? It seems odd that they are all shown as changeover relays but without the terminal to the normally closed contacts?

Alec

[dazzer]

Just a footnote to this. Do not purchase a modern Lucas 6RA. They look good and thats the only purpose they serve. Find a used example if you want 6RA. My last one was a 1964 article original on my 65 2000. It only finally packed up end of last year. I replaced with a modern Lucas 6RA... first one was dead, replaced with a second... lasted two days. Returned and replaced with a modern durite. Still working perfectly.  
Just my experience
Cheers
Dazzer

[Greta]

Quoted from JohnD

Coming late to this, but to point out that a multimeter and a little understanding of what happens in a relay, will let you work it out.

For relays that have four terminals, two are the coil and two for the feed and supply to the unit to be switched.
Only the first pair are in continuity on the bench, so set your MM to resistance, or "continuity" if you have it (it will bleep if you touch the probes together) and test the terminals.
One pair will show that they are connected - that is the coil and should be wired to the switch on your dashboard or whatever.

The other pair are to be wired to a supply and to the unti to be powered.

Simples!
John

PS circuit diagrams of the Lucas 6RA relays are readily available online.

So John according to your diagrams the +12v input feed ( my brown wire) from the starter solenoid should be connected to C2 and the out feed to the O/D Solenoid should come from one of the two C2 terminals - leaving one redundant.

Does this suggest that either SRB 111 or  SRB 121 are the correct 6RA relays !? If not which?

[TedTaylor]

Quoted from piman

Hello John,

are those Lucas relay diagrams? It seems odd that they are all shown as changeover relays but without the terminal to the normally closed contacts?

Alec

The diagrams John has posted are OK - no need for a connector on the resting/open side.  They are not changeover type, all are normally open.  

I suppose the fact that the 'resting' non contact side is shown the same as the contact side is confusing.

MUT

[TedTaylor]

Quoted from Greta

So John according to your diagrams the +12v input feed ( my brown wire) from the starter solenoid should be connected to C2 and the out feed to the O/D Solenoid should come from one of the two C2 terminals - leaving one redundant.

Does this suggest that either SRB 111 or  SRB 121 are the correct 6RA relays !? If not which?

It relates to the resistance of the coil as marked alongside it.  I am pretty sure it would be 70 ohms so SRB 111 would be correct, I think the lower resistance SRB 121 is a smaller more compact relay rarely used on 'our' age cars.

To identify which wires to use simply remember that the operating current, i.e. feed to the coil or 'W' only needs to be low current - typically about 5amp on our cars.  Identify it as a wire with only 9 copper strands.

The contacts 'C' are to carry heavier current so would be for thicker cable - typically wires with 14 or more copper strands. And what goes out has to come in so are usually similar size thick wires.

However with SRB501 where C1 is 'commoned' with the coil feed this wire would be slighty heavier, probably l4 strand, as it must be able to carry the current for the out contact C2.  It is used to simplify the wiring but not meant for heavy duty application such as headlights, heated rear or front window, or something with a motor etc. (I made that mistake many years ago 🤔 )

Please remember that much of the wire we buy today is of the thin wall insulation type with thinner copper strands but more of them.

MUT

(Sorry John for butting in)

[Hogie]

Quoted from Greta

Thanks guys - it was wired correctly so I guess the relay really is goosed.

That's the clearest wiring diagram I've ever seen. ( Have you a similarly clear diagram that shows how to convert from Dynamo to Alternator - the clearest online diagram I could find doesn't match the rather garbled instructions posted with my dynastar.


Just for completeness - Can one use the more modern cube type relay - if so what are the equivalent terminals?

Hi Greta,
           yes you can use a modern relay  http://www.vehicle-wiring-products.eu/product.php/642/12v-4-blade-relay
Durite   Four blade 'A' type would do it ncey.

Roger

[JohnD]

If you just look at the link Hogie provided, the page from Vehicle Wiring Products, there is a wiring diagram on the relay!

The nomenclature of the terminals on the modern relay is according to the DIN 72552 standard, that long ago superceded Lucas, and is now industry standard.
See the list here: http://www.bosch-classic.com/m.....menbezeichnungen.pdf in English!

The DIN system is organsied in a different way, as you will see,  For instance, any "line from battery positive" is a 30.
85 and 86 are the coil terminals, 86 is the supply;   the line out to the unit to be switched is 87.

All very logical, Nicht Wahr?

John

[Saltddirk]

The only issue with how Triumph did the OD wiring is that the OD relay is switched by putting it to Earth. (switch in the earth side of the relay) If you have any wiring shaving through and making contact with earth then the OD engages, which might not be as you want. The inhibitor switch on reverse should prevent the OD from engaging in reverse, but that one can fail too. If you put the switch in the lead from ignition then if you have a ground fault either, nothing happens (ground fault in the earth side) or you blow a fuse (ground between relay and switch).

Dirk

[piman]

Hello Ted,

I don't believe that any manufacturer would actually use a contact as a resting place for the moving contact, certainly all the industrial relays I've seen do not have them. It all adds extra cost for no purpose?

Alec

[TedTaylor]

John and Hogie's comments suggest (to me) an interesting point.

The switching current on a Lucas 'can' relay is 30amp.  Adequate for most normal original spec uses but can be stretched if using some modern lighting so worth double checking the current draw when they are used.  For reliability I would suggest maximum total load of 25amp.

However modern plastic box relays as standard are designed to switch 50amp ....... or more in certain high current relays.  So well up to most uses but still if doing something fancy just do a quick check.

The advantage with the Lucas relay is originality especially if on view under the bonnet and appearance matters. On the Mk1 PI estate I would never use a modern relay.  And similarly AFH my very early Mk1 2000 which I prepared as a rally car starting in 1991 - doubling up on Lucas relays if there was likely to be a loading problem

On the other hand Woodie has no pretensions to be a rare interesting Mk2 - just a great car to enjoy and have fun with.  Lots of upgrades and fitting relays was simple - plastic box ones all the time.

[TedTaylor]

Quoted from piman

Hello Ted,

I don't believe that any manufacturer would actually use a contact as a resting place for the moving contact, certainly all the industrial relays I've seen do not have them. It all adds extra cost for no purpose?

Alec

I am not suggesting that - just trying to explain simply that the way the person who drew the points in those diagrams has made it a little misleadiing ......... as had happened. 🤔

MUT