Morris Minor Owners Club

microbill55 wrote: ↑Sat Nov 01, 2025 6:00 pm 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.......

There have been lots of threads about faulty new flasher units going back years. Why something so apparently simple has to be a total nuisance I have no idea!

The insides of the new Lucas SFB100 have a black plastic box thing that is a relay and that is what makes a soft click. It doesn't use the bimetallic strip and heating wire of the original FL5. In fact, the FL5 has two armatures, one for the indicator bulbs on the outside of the car and another for the tell-tale lamp.

If interested here is some info on the original Lucas FL5: viewtopic.php?p=707584&hilit=Lucas+fl5#p707584

Stephen

As I suspected, this is what I found.......

Just to expand a bit, having confirmed that these units are indeed electronic, I will nevertheless try the matching one I bought from Bill's supplier, who knows, it may work. Brakes are back together now, so if the rain ever stops I'll try it out.
In the meantime, I'm still looking for a FL5 thermal/bi-metallic flasher, so if anyone knows of one for sale, please let me know.
Regards Bill.

microbill55 wrote: ↑Tue Nov 04, 2025 4:28 pm Just to expand a bit, having confirmed that these units are indeed electronic, I will nevertheless try the matching one I bought from Bill's supplier, who knows, it may work. Brakes are back together now, so if the rain ever stops I'll try it out.
In the meantime, I'm still looking for a FL5 thermal/bi-metallic flasher, so if anyone knows of one for sale, please let me know.
Regards Bill.

Bill, I've sent you a PM

Stephen

There is one her at a reasonable price but states 36W.

https://www.britishbikebits.com/lucas-f ... l5-12v-36w

mobylette wrote: ↑Tue Nov 04, 2025 5:23 pm There is one her at a reasonable price but states 36W.

https://www.britishbikebits.com/lucas-f ... l5-12v-36w

It needs to be 12 volts 42 watts

There are numerous variations including 6v, 24v and many wattages.

Stephen

Bill, can i suggest taking one the flasher units and wiring up 2x21w bulbs separate from your car body, then power from your cars battery directly, poss and neg, check flash rate,then run engine and see if any effect on flash rate.
You can solder wires direct to the bulb if you don't have spare holders as it only for test just wrap in electrical tape.
I still don't understand that electronic or bi-metallic type the flash rate is effected only when driving

Bill_qaz wrote: ↑Tue Nov 04, 2025 6:07 pm
I still don't understand that electronic or bi-metallic type the flash rate is effected only when driving

The implication is that the Ignition system high energy arc is interfering with the electronics of the timed switching of the output, which to me indicates poor design of the Flasher unit if it is doing that....

geoberni wrote: ↑Tue Nov 04, 2025 8:08 pm

Bill_qaz wrote: ↑Tue Nov 04, 2025 6:07 pm
I still don't understand that electronic or bi-metallic type the flash rate is effected only when driving

The implication is that the Ignition system high energy arc is interfering with the electronics of the timed switching of the output, which to me indicates poor design of the Flasher unit if it is doing that....

I still have doubts Berni, I have virtually the same set up,electronic ign etc, with can on inner wing( see earlier post pic) and have never had an issue. That why i made the suggestion to separate it from vehicle wiring.

I don't understand it either. The king lead in my car is not suppressed at all (it is copper cored HT cable). The HT leads to the sparking plugs are also copper cored but do have resistive plug caps. I have electronic ignition (Lumenition Optronic) but I don't have an alternator. Thermal FL5 units work perfectly in my car, electronic units I have tried only work if they are the type with a separate earth lead but as my car is POS earth, they have to be the correct polarity. I have tried quite a few modern flasher units as I wanted a spare that actually worked. In the end I sourced another NOS FL5. The modern electronic types with a separate earth lead work well but look completely wrong.

What happens if the indicators are switched on with the engine running and the engine revs are gradually increased with the car parked? It's easy enough to adjust the idle screw on the carb to increase the revs and then look at the indicators front and rear or just ask an assistant to help by pressing the accelerator pedal. Could there be arcing at the distributor rotor. Has the OP checked this? Does it looked burnt?

What about measuring the voltage at terminal B (on more modern units this is X) on the flasher can as the revs are increased?

Stephen

The indicators speeding up can also be caused by a bulb failing, is it possible that there is a loose connection, or short, that only shows up with engine vibration? Can you ask an assistant to follow you to check if all the indicators are actually working as you drive along.

panky wrote: ↑Tue Nov 04, 2025 11:10 pm The indicators speeding up can also be caused by a bulb failing, is it possible that there is a loose connection, or short, that only shows up with engine vibration? Can you ask an assistant to follow you to check if all the indicators are actually working as you drive along.

The op said he's had someone infront and behind observing in his earlier post

Ah missed that

If the OP thinks the strange behaviour of the flasher unit is caused by RF interference from the ignition system there is something he could try.

I may be wrong, but the electronics of the flasher unit are inside a metal can and usually that metal can is connected to earth via the mounting to body. The unit does not require an earth in order to function but the earthing would surely protect the electronics from RF interference?

Perhaps there is too much noise on the input to the flasher unit. Could he try one of these ferrite ring core RFI suppressors?

It would be better though to identify where the interference is coming from. It could be a fault that should be corrected.

https://www.classiccarleds.co.uk/produc ... 22fe&_ss=r

Stephen

Bill_qaz wrote: ↑Tue Nov 04, 2025 11:32 pm

panky wrote: ↑Tue Nov 04, 2025 11:10 pm The indicators speeding up can also be caused by a bulb failing, is it possible that there is a loose connection, or short, that only shows up with engine vibration? Can you ask an assistant to follow you to check if all the indicators are actually working as you drive along.

The op said he's had someone infront and behind observing in his earlier post

I may be wrong, as this is quite a long thread to go back and re-read, but I thought he said it was his intention to have someone out on the road in another vehicle to observe, not that it has actually been done....

Only he knows, perhaps an update is needed on the many many suggestions
He says he also tried moving flasher can inside vehicle away from ignition system which is only standard points, so rf seems unlikely.

I'm wondering if we are being lead along a false path with this RF interference subject...
Let's get back to basics.
So it happens on a 'drive around the block' which to me implies not very far.
Just leave the car stationary and rev it up to 'driving revs' and have the indicators going.
With the car actually moving, the only real thing different from revving it outside the house is the random bumps in the road. Pot holes shouldn't produce a consistent change in indicator flash rate...

It should be possible to reproduce while stationary.

A bit of a long shot, but I would connect a multimeter to the Flasher input to check the voltage (I know it was previously said the Alternator is a consistent 14.3 v), but after confirming that DC reading at higher revs, change the setting to measure AC and see how much ripple is present on the DC, there might be a problem with the Diode pack on the Alternator. That could be messing with the electronic flasher.

Sorry guys, having trouble posting. Have lost 2 very detailed replies to all comments. Rest assured I'll try them all.
Regards Bill

geoberni wrote: ↑Wed Nov 05, 2025 11:16 am I'm wondering if we are being lead along a false path with this RF interference subject...
Let's get back to basics.
So it happens on a 'drive around the block' which to me implies not very far.
Just leave the car stationary and rev it up to 'driving revs' and have the indicators going.
With the car actually moving, the only real thing different from revving it outside the house is the random bumps in the road. Pot holes shouldn't produce a consistent change in indicator flash rate...

It should be possible to reproduce while stationary.

A bit of a long shot, but I would connect a multimeter to the Flasher input to check the voltage (I know it was previously said the Alternator is a consistent 14.3 v), but after confirming that DC reading at higher revs, change the setting to measure AC and see how much ripple is present on the DC, there might be a problem with the Diode pack on the Alternator. That could be messing with the electronic flasher.

Yes that's pretty much what I said on Tuesday except I didn't suggest checking AC

Stephen

svenedin wrote: ↑Wed Nov 05, 2025 11:20 am
Yes that's pretty much what I said on Tuesday except I didn't suggest checking AC

Stephen

Sorry, missed that I've been trying to make sense of it all...
I'm trying to think a little outside the box as it's a very strange scenario. I can't even get my head around the info from Classic Car LEDS, saying that RF interference can affect the Electronic Flasher Unit. To me that's a issue with the flasher design....