Morris Minor Owners Club

Hi all, hope someone can shed some light on an indicator problem. I'll explain, My car '61 Traveller, neg earth, alternator conversion, has had the trafficators removed and now has indicators. When doing this I used an electronic relay for longevity. Everything works as intended whilst the engine is off, it's also ok on startup, however, if I drive round the block the indicators flash at double speed!!
I wondered if engine bay heat could be the problem, so re-located the relay behind the drivers glovebox, alas, no change to the problem. I think the solution is to change to a thermal relay (FL5), so have ordered one from ESM. My only answer to this problem is possible EM interference from the (standard) ignition system or too high a charging voltage at higher revs ( although the voltmeter shows max 14.3v. Is this feasible? All earth connections checked and ok.
Any thoughts would be appreciated, as not knowing is annoying.
Bill

Are you using an electronic version of the standard 3 pin flasher can? If so I used one of these but it had an additional earth lead during my brief dalliance with LED indicator bulbs. I had no luck with electronic 3 pin flasher units without the additional earth connection. It worked perfectly but I decided to go back to an FL5 and standard incandescent bulbs for originality reasons. I am positive earth.

Stephen



https://www.classiccarleds.co.uk/produc ... -p-2-3-pin

Note this warning: IF THE RELAY DOES NOT BEHAVE WHEN THE ENGINE IS RUNNING YOU NEED TO ADD SUPPRESSION TO THE LEAD BETWEEN YOUR COIL AND DISTRIBUTOR TO REDUCE THE RF INTERFERENCE.

Thanks Stephen, for the quick reply. It is a 3 pin (X,L,P) so no earth connection. It's a plastic enclosure with plastic moulded fixings tag. All my bulbs are incandescent, except for a fog lamp and high level third brake light, which were added for safety/visibility reasons,. There is no difference to the double flash rate if either or both are on at the same time.
I bought the relay from Car Builder Solutions and they have never heard of this before.
Has the FL5 solved your issues? It sounds like the simplest solution, so I'll give a go.
Still like to know the cause as it's bugging me, Grrr.!

It may be as I posted above (below the link for the electronic 3 pin flasher with an earth lead) that it is RF interference from the King lead between coil and distributor.

I had perfect operation from the 3 pin flasher unit with an earth lead in the link above. I only changed back because I fitted a new loom and repainted the engine bay so I wanted it to be as original as practical.

I found electronic 3 pin flasher units without an earth lead (so-called FL5 equivalent) did not work (even when they specifically stated OK for POS earth)

Yes, I fitted a new old stock thermal Lucas FL5 and it worked perfectly. The only trouble being that people seem to think these demand collectors item prices so shop around wisely! Also ensure exactly the correct FL5 variant. There are 6v and 12v versions with different wattages. It MUST be FL5 12v 42w (+3w). Each indicator bulb is 21w so 42w for both bulbs per side and nominally 3w for the tell-tale bulb (pilot). It may not mention (+3w) on the flasher can. That doesn't mater but 12v 42w does matter.

Or a modern copy is OK as long as it's thermal but not sure about longevity of these. Lucas SFB100 or Lucas SFB105 and equivalents.

Stephen

Hello, unfortunately I seem to still have the problem described above.
I ordered a Lucas SFB100 from H Bowers thinking it was thermal, but turns out it's electronic.
I spoke to them and they suggested their product code BRP 502096, just described as a Lucas flasher unit. They thought this unit was thermal.....is it? It doesn't work anyway!
So, my question is, where can I get a genuine FL5 (that doesn't cost the earth), thermal unit for negative earth cars?
There is a unit on eBay, new old stock, (allegedly ), but it looks a bit scruffy.
I'd rather purchase from a reputable dealer, with some technical knowledge, just in case. As a point of info, the guys are Bowers admit to not really having the required in depth knowledge, as they only buy in and resell, so are naturally reticent to offer any advice.
Bill
.

Don't know if genuine but bought and fitted Jan 2022 to replace faulty one and has worked perfectly to date on standard bulb indicators neg earth.
https://ebay.us/m/KDkgfc

Thanks Bill, but it's an SFB100, which is electronic and flashed at double speed when I drove the car, I think due to EMI/RFI interference from the ignition system, but could be something else??
The logic behind my wish to use a thermal/bi-metallic flasher, rather than suppressing the king lead, is to not to detrimentally affect the (standard) ignition system in any way. I already have carbon HT leads, which effectively are already suppressed. As I am not sure where the interference actually emanates from, it seemed easier to use an "old school" solution.
Any other possible solutions??
Bill

That's odd. I thought the Lucas SFB100 was thermal because it is not polarity sensitive.

The trouble with buying a NOS Lucas FL5 (which is definitely thermal) is that they can be described as "working" (meaning the indicators will flash) but the flash is not necessarily at the correct legal flashing rate (60-120 flashes per minute).

Stephen

microbill55 wrote: ↑Wed Oct 29, 2025 7:01 pm Thanks Bill, but it's an SFB100, which is electronic and flashed at double speed when I drove the car, I think due to EMI/RFI interference from the ignition system, but could be something else??
The logic behind my wish to use a thermal/bi-metallic flasher, rather than suppressing the king lead, is to not to detrimentally affect the (standard) ignition system in any way. I already have carbon HT leads, which effectively are already suppressed. As I am not sure where the interference actually emanates from, it seemed easier to use an "old school" solution.
Any other possible solutions??
Bill

I don't believe its electronic as they flash at a fixed rate regardless of load, hence can be used with led, I think this unit is for incandescent bulbs only as rated 2x21w bulb. According to Internet.
The Lucas SFB100 flasher unit is a thermal flasher unit, not an electronic one. It uses a mechanical, bi-metallic strip that heats up and cools down to create the blinking action, which is what produces the distinct clicking sound associated with older vehicles. 

1 x Lucas 12V 42W 3 Pin Flasher Unit
Specifications:
12V
Supplied in Genuine Lucas packaging
Can be used with both positive & negative earth vehicles

Full spec is in the ebay advert if you want to check.
I have no affiliation to the seller

I have been away so I wasn't able to access the forum.

The Lucas SFB100 is a thermal flasher unit. It isn't electronic. It is a standard 12v 42w flasher unit. It can only flash 2x incandescent bulbs of the correct 21 w wattage simultaneously. It is very important that the indicator bulbs are the correct wattage or the flash rate will be incorrect. The load must be correct or it affects the heating of the bimetallic strip inside the flasher can which affects the flash rate.

The OP's car has been converted from semaphore indicators to flashing indicators but how has this been done? Have extra amber lights been fitted front and back or is it flashing the stop lights? We need more information. What kind of indicator switch is it using? The same one that operated the semaphores? Apparently the flash rate is OK until the car is being driven but then the flash is rate is double speed. Is this something to do with the engine running, the alternator conversion or the concurrent use of the brake lights when braking? With the standard thermal flasher relays like FL5, the flash rate goes too fast when a bulb has blown. Is an indicator lamp not working when the car is being driven? Bad connection? If it's a failing bulb or bad bulb/bulb holder connection the fault would only occur when indicating to one side not both.

I would be inclined to check all 4 indicator bulbs, replacing any that are blackened or showing abnormal resistance readings or a saggy filament; clean all the bulb holders to bright metal; check lamp fitting earths; trace all of the wiring and check connections wherever there are joins/bullet connectors. Bad earth connections can cause strange faults.

Stephen

Ok, many thanks, your points noted and gratefully received.
The reason I believed that the SFB100 supplied by Bowers, was electronic is
(a) The delivery note stated electronic SFB100, even though I had ordered a thermal unit.
(b) When I queried this, they confirmed this and suggested the alternative BRP502096. See previous post regarding their (lack of) technical expertise.
(c) When temporarily connected, it mirrored the behaviour of the originally installed known electronic unit. Are these units genuine Lucas, or copies?
So, the conversation to indicators uses the original steering column switch (stalk pilot bulb removed) as a dash repeater (3W) was preferred. All new rear bulb holders, bulbs (21W incandescent clear), amber glass lenses. Front are new bulb holders, bulbs ( 21W incandescent amber), clear glass lenses housed in the former side light position. Dash repeater is powered from P terminal on flasher unit. All indicator wiring is independent of brakes etc. The flasher unit X terminal is fed from a sub fuse to the ignition "on" fuse. Front and rear indicator earth wiring is run back to a dedicated earth stud, adjacent to the battery,i.e. not via a body/chassis connection.
Everything works as designed when the engine is off. Initially, on startup, all is still ok. Driving the car (higher revs, road vibration, higher charge rate), causes double speed flashing, irrespective of turn selected. It would seem to suggest the fault lies with the flasher or it's immediate wiring.
I will perform a road test with a lead/ following car to check indicators illuminate when selected ( even if it's at double speed), to eliminate poor connections as a possibility. If they work, they work, even though the speed is double. In addition, I will re- check, for the third time, all bulbs/ connections/ wiring and confirm earth continuity.
The alternator conversion was installed using the ESM kit and is functioning correctly, with consistent 14.3 v charge voltage. I haven't driven far enough to monitor the guage over a long timespan.
Stephen could you post details of your supplier of the FL5? I think I'll order one from the link supplied by Bill too, so I'll have a spare.
Once a known thermal relay is fitted it will, at least, eliminate EMI/RFI as a cause.
Bill

I bought a few original NOS Lucas FL5 over the years from various eBay sellers or at auto jumbles.

ESM sell 3 different types of flasher unit. Two types are electronic and specify for negative earth only. One type would appear to be thermal and is dual polarity. This is the thermal one: https://www.morrisminorspares.com/elect ... as-p829875

Or Autsparks state this one is "mechanical" but they don't specify the load rating: https://www.autosparks.co.uk/electrical ... sher-relay

I have a spare Lucas SFB100 from ESM. I will test it right now and check if it is definitely mechanical


Stephen

I just tested a Lucas SFB100 from ESM on my car. This came from ESM a few weeks ago as I thought I ought to have a spare. It definitely IS mechanical but it doesn't work properly. The indicators flash as expected and it makes the familiar ticking but the pilot lamp does not work. I reconnected my original Lucas FL5 and everything works. New flasher is going to be returned to ESM.

Stephen

Bill, I have same set up amber independent flasher on rear, amber replacement of the original front side lights(now in headlights)
Alternator conversion, my flasher can is drivers side inner wing not far from distributor (pertronix ignition) the only difference is I am using original green warning light on stalk. All with the flasher can I referred you to with no issues.
Silly question maybe but are the indicators high speed flashing or just the warning light ?
You can unplug the warning light spade without effecting flasher just as a tes
When they double flash is any other lights being used, are your brake lights operating?
Do you have four way flashers, if so do they behave normally, they use their own flasher unit for 4 times 21w.

Thank you both for the speedy responses. Stephen that's very interesting regarding the recently purchased SFB 100. Perhaps there is a bad batch out there. Maybe the one I had was faulty too.
Bill, your install is very similar to mine and I too had the flasher in the engine bay, but relocated it to behind the drivers glovebox, as I thought my original (electronic) flasher was playing up due to excess heat. This didn't stop the double speed flash, hence my mention of EMI/RFI being a possible cause, affecting the electronics in that particular flasher. Obviously, changing to a known good thermal unit, eliminates (?) electrical interference as a cause. The pilot dash light flashes in sync with the others, it behaves exactly as the main flashers.
I have just installed hazard lights, using a FL9 thermal 2 pin flasher rated at 98W, but have not yet tested this on the road ,as my brakes are currently in bits due to a weep at the master cylinder (posted in mechanical), but that's another story. The FL9 works a treat with the engine off and was installed after the double speed flash occurred so not had a chance to see if it's affected, hopefully not. It's definitely a thermal relay, as I can actually feel the switch operating. It also makes a very nice clunk as a bonus!
I just need to buy and fit a known good thermal FL5, to put the EMI/RFI theory to bed. I have considered using a second FL9 for the flashers, but it's not the correct wattage, plus I would lose the repeater ( this can be done using a relay from the L pin, I believe).
I don't have the knowledge to say if this option would work.
Bill, given Stephens experience with ESM, I may buy 2 from your supplier. I am tempted to pull one of them apart just to see inside.
Your comment regarding the brakes is valid, but the flash rate is unaffected when braking.
You mention that you have Petronix ignition, which is electronic, isn't it. I have considered changing my points to electronic, maybe, if the problem is my ignition system, that's something to consider in the future.
Again, thanks for your help.
Bill

Here is one I destroyed earlier.......

This is a Lucas SFB100 from ESM that I received a few weeks ago. It doesn't work properly and ESM have agreed to replace it. They told me they didn't want the faulty unit back so I took it apart. As you can see, it is NOT thermal.....

Stephen

Stephen does it make the audible click of the thermal type?
I notice the end plate is black, mine is brown, i wonder if thats relevant in identification? Not good if marketed as Lucas sfb100

Bill_qaz wrote: ↑Fri Oct 31, 2025 6:51 pm Stephen does it make the audible click of the thermal type?
I notice the end plate is black, mine is brown, i wonder if thats relevant in identification?
20250213_151437.jpg

Not good if marketed as Lucas sfb100

It makes a click but not like my old FL5. I suspect the "click" is being made electronically.

Stephen

svenedin wrote: ↑Fri Oct 31, 2025 7:09 pm

Bill_qaz wrote: ↑Fri Oct 31, 2025 6:51 pm Stephen does it make the audible click of the thermal type?
I notice the end plate is black, mine is brown, i wonder if thats relevant in identification?
20250213_151437.jpg

Not good if marketed as Lucas sfb100

It makes a click but not like my old FL5. I suspect the "click" is being made electronically.

Stephen

It must have an electronic click, hence difference in sound from mechanical.

Oh no! I hope the two I've ordered aren't the same. I'll post a photo of the one I take apart. It does explain why the SFB100 from Bowers didn't stop the double flash rate.
To be continued.......