Lucas flasher unit connections

[JAD337]

Hi, hope someone can help. I have a 1955 Minor which just had trafficators when I purchased it. I would like to add flashing indicators and I have a copy of the AutoSparks wiring diagram that illustrates what is required. I have purchased 4 flasher lights and because the car is positive earth I have obtained the Lucas SFB100 flasher units. I have taken a lead from each of the outputs from the trafficator switch. I then decided to test the rest of the wiring before going any further.
The terminals on the Lucas unit are marked L P and X, with no clear indication of what is connected to each one. The wiring diagram only shows 2 connections to each relay. I assume the third one is to earth. I tried what I thought would be correct, with no success. Since then I have tried all the other permutations and the only one that achieves anything useful is:-
X to trafficator switch
P to flasher light
L to earth
The result was the flasher light came on but didn't flash.
Any ideas where I am going wrong?

[svenedin]

P= pilot. The dashboard lamp that tells you the indicators are on
L= load or lamp as I remember it, flashed output
X= power in

No terminal on the flasher unit is connected to earth. If P is not required it can be left unconnected

If the Lucas SFB100 is thermal then the polarity does not matter. If it’s electronic, X and L may need swapping round

It sounds as if you could have used 2 pin flasher units. These are cheaper. These are very simple and all they have is a live feed in and a flashed output.

My car is positive earth but it's a late car and it has never had traficators. Late cars just use a single 3 terminal Lucas flasher can, FL5. This is thermal (bimetallic strip) and not polarity sensitive (or at least the old ones are). P in late cars is connected to the bulb at the end of the indicator stalk.


Stephen

[JAD337]

Thanks for the explanation Stephen. I tried using X and L and nothing happened on the light. I then tried the other relay and success, a flashing light connected to the X terminal. The relay I used yesterday must be either faulty or damaged from yesterday's testing - is it possible to damage them by incorrect connections?
Either way, I will get a replacement and continue the project. Your assistance is very much appreciated.
John

[svenedin]

Thanks for the explanation Stephen. I tried using X and L and nothing happened on the light. I then tried the other relay and success, a flashing light connected to the X terminal. The relay I used yesterday must be either faulty or damaged from yesterday's testing - is it possible to damage them by incorrect connections?
Either way, I will get a replacement and continue the project. Your assistance is very much appreciated.
John

Hello John. You're welcome. I only know the basics with the car electrics. Berni is the man for electrics.

If you switch X and L you won't damage to the flasher unit even if it's an electronic one BUT if you had P connected to earth directly and the other connections wrong you probably burnt it out inside.

If you are able to it is highly desirable to make your new wiring in the correct colour coded (Lucas BS-AU7) wiring. You can buy the cable in (almost) all of the different colours or wiring can be harvested from inside (where it is protected) old wiring looms. Using the right colour code means it is really simple to trace your new wiring e.g green/white goes to right hand flasher lamps; green/red goes to left hand flasher lamps. Where things become highly problematic is where somebody has made all the new wiring in black wiring especially because black is the colour for an earth connection!

Stephen

[JAD337]

Thanks Stephen.
Totally agree about the cable colours, my car looks to have had some rewiring done, and using black cable!
I have already purchased green plus green and white cable for doing this project.
John

[mike1864]

Aside from P, L and X, I believe this relay has a fourth connection, which no-one has mentioned.
It's the cannister itself!
I reckon it will not work unless the mounting tab is screwed into the bodywork, providing a grounding path for the heating element/electronics.
Has the OP been experimenting with the cannister just lying around loose?

[svenedin]

Thermal flasher relays do not earth from the canister. Nor do the electronic types that look like the thermal flasher cans unless they specifically require an earth which is usually provided by a fourth pin.

See FL5:

https://www.lrsoc.com/forum/forum_files ... al%20K.pdf

[mike1864]

I see where my confusion arose.
Three years ago I bought a flasher relay from Mini Spares, expecting its 3 pins would make it equivalent to my old (metal cased) one, that had just gone faulty.
But it arrived in a plastic encapsulation with no instructions as to the function of of the three pins, marked 31, 49 and 49a. And I could see that the slide-in mounting tab was clearly not connected to any of the internal workings.
I took a guess at correlating P, L and X with the markings, but no configuration would make it work.
Some online research then revealed that 49 was the battery, and 49a was the lamps.
There was no provision for a pilot lamp; pin 31 needed to be earthed.
I concluded that this sort of relay doesn't need a load for it to operate. But it was useless for a car with a pilot lamp.
And I (wrongly) surmised that my broken relay similarly relied on an earth, through its case.

[geoberni]

Hi

let's see if we can clear this up for you...

Hi, hope someone can help. I have a 1955 Minor which just had trafficators when I purchased it. I would like to add flashing indicators and I have a copy of the AutoSparks wiring diagram that illustrates what is required. I have purchased 4 flasher lights and because the car is positive earth I have obtained the Lucas SFB100 flasher units. I have taken a lead from each of the outputs from the trafficator switch. I then decided to test the rest of the wiring before going any further.
The terminals on the Lucas unit are marked L P and X, with no clear indication of what is connected to each one. The wiring diagram only shows 2 connections to each relay. I assume the third one is to earth. I tried what I thought would be correct, with no success. Since then I have tried all the other permutations and the only one that achieves anything useful is:-
X to trafficator switch
P to flasher light
L to earth
The result was the flasher light came on but didn't flash.
Any ideas where I am going wrong?

So, working from the parts I have highlighted...
I'm assuming your car has not been modified regarding the trafficators installation and you have a Lucas SPB120 switch, probably by your knee if in the original location.

SPB120.JPG (27.85 KiB) Viewed 23040 times

The Autosparks diagram uses 2 PIn Flasher Units, you've brought the SFB100 which are 3 Pin. Traditionally speaking this doesn't matter, so long as the correct one is left disconnected, but there can be exceptions with the modern electronic ones. They sometimes don't like the Pilot being left disconnected.
The traditional Bi-metal heater type, with 3 pins, just has a separate output to the Pilot Light, but the electronic ones depend on their design.
As Stephen said, the connections are :
B or X= power in
L= load or lamp as I remember it, flashed output
P= pilot. The dashboard lamp that tells you the indicators are on
As you can see here (Only 1 side shown - it's only how you would connect to test it's operation), regarding it's operation, it's irrelevant having the P connected.

Traditional Bi-Metal Flasher 3 Pin.JPG (15.29 KiB) Viewed 23040 times

I see from your latest comment that you're now talking a modern 3 Pin Plastic case thing, not "Lucas SFB100", or are you just trying to relate that past experience to the Lucas 'SFB100'....

I see where my confusion arose.
Three years ago I bought a flasher relay from Mini Spares, expecting its 3 pins would make it equivalent to my old (metal cased) one, that had just gone faulty.
But it arrived in a plastic encapsulation with no instructions as to the function of of the three pins, marked 31, 49 and 49a. And I could see that the slide-in mounting tab was clearly not connected to any of the internal workings.
I took a guess at correlating P, L and X with the markings, but no configuration would make it work.

There's many different Flasher Units out there, but they have different model numbers and configurations... Some of them don't require a load for them to operate, some do.

If you have genuine 'modern electronic' Lucas SFB100, they should not be polarity sensitive but it depends on who you brought them from.

To test them connect up as per the diagram above, Supply to X(B), Load of 2 lamps on L and a small pilot lamp of around 5w on P.
Let us know how you get on.
If they work, disconnect the pilot lamp from P and see if it still works, I suspect it may not...

[mike1864]

To avoid confusion, it was me (Mike1864) who referred to having a plastic relay, not the original poster (JAD337).
Incidentally I've just dismantled an old - metal cased - flasher, and can confirm that the case indeed has no connection to the workings.
Apologies for my red herring earlier!

[geoberni]

To avoid confusion, it was me (Mike1864) who referred to having a plastic relay, not the original poster (JAD337).
Incidentally I've just dismantled an old - metal cased - flasher, and can confirm that the case indeed has no connection to the workings.
Apologies for my red herring earlier!

Opps, speed reading the post and not paying attention to the person posting it.
Just read the content and misinterpreted the connection.

Correct, there is no need for an earth on the traditional/conventional Flasher, it is just a metal canister around a little heater/switch assembly. The earth of the circuit is via the lamps.

[mike1864]

And of course the type than NEED an earth generally incorporate a relay that feeds the lights with raw 12 volts (ie not via an element).
This has the advantage that the unit doesn't care whether the bulbs draw 3.5 Amps (incandescent) or 50 mA (LEDs).
But it has the disadvantage (as in my plastic DRC8626) that it gives the driver no indication of a blown bulb(s); no pilot feed, and it happily clicks away regardless.
That said, there might be a variant that somehow provides this, but because I have filamented bulbs, I've not looked into it.

[mike1864]

While on the subject, my existing flasher's clicks are too quiet.
So I wired in a buzzer, mounted behind the dash, that buzzes in sympathy with the bulbs' illumination.
But this a bit too intrusive, especially at low speed, or stationary.
Does anyone know of a standalone 12V device that clicks as loud as on modern cars, to replace the buzzer?

[geoberni]

While on the subject, my existing flasher's clicks are too quiet.
So I wired in a buzzer, mounted behind the dash, that buzzes in sympathy with the bulbs' illumination.
But this a bit too intrusive, especially at low speed, or stationary.
Does anyone know of a standalone 12V device that clicks as loud as on modern cars, to replace the buzzer?

I'm guessing your Flasher Unit is in the engine bay as that's where factory fit one was. I guess it depends on the noise levels in your car, mine's pretty noisy as there's no insulation material under the carpet, something I'll get around to resolving at some point.

I suspect you've fitted some sort of towing repeater buzzer??

Modern relays tend to be a bit miniature and often therefore too quiet, but an old traditional relay wired to the Flasher Unit, mounted to the metalwork of the dash should give a firm clunk every operation.
I'm not sure if the current draw might affect the ability to tell if you have a bulb gone though

Alternatively, if the existing Flasher does give a firm click, but you just can't hear it inside the car, rig it up with a couple of extension wires and temporally fit it under the dash. If that's good enough make it permanent.

[mike1864]

Yes, the (too quiet anyway) flasher unit is mounted on the engine bay bulkhead, next to the fusebox.
And the current buzzer is just a general purpose one from Maplins.
I believe I put it across the pilot lamp feed; so it shouldn't affect the bulb monitoring aspect.
What I'm really after is something that is designed to make clicks (going tick-tock?), rather than the sound being a by-product of relay contacts making.
I could knock something up with a solenoid and blocks of wood, but I'd rather source something ready packaged!
A sudden afterthought; perhaps a miniature speaker (with a series resistor!)

[StillGotMy1stCar]

It would be better to use a capacitor in series to stop the DC, It would still click or pop but with reduced current flow that would damage the speaker. Perhaps a 470uf at 16 or 25V would be suitable, make sure you connect it up with the correct polarity. You could still add a resistor if the click is too loud. Worth a try, it could be an interesting noise.

Regards John

[svenedin]

What you could do is leave the original flasher can on the bulkhead for an original appearance but make it redundant by fitting another (operational) flasher can under the driver's side dashboard. You can just use a Lucas FL5 type exactly the same as the original and it will tick tock happily but where you can hear it. Or if you want to use LED indicator bulbs you could fit an electronic flasher relay under the dash. There is a selection here (polarity sensitive): https://www.classiccarleds.co.uk/collec ... nic?page=1 There are usually vacant holes in the bulkhead that you could use to feed extension cables from the redundant bulkhead flasher to your new one, following the BS-AU7 colour coding of course!

Stephen

[Bill_qaz]

They advertise one with the OE click thats works on bulbs or led
https://www.classiccarleds.co.uk/produc ... 3GMYbW7cH5