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MG MGB Technical - Replace both flashers?

Hi All!
I couldn't find an answer in the archives...I'm converting to LED bulbs for the turn signals, I know I have to get a new electronic flasher for the turn signals as the LEDs don't generate enough heat to operate the bi-metalic I also need to replace the Hazard flasher? I have a 69 Roadster.
Bob D
Bob Dougherty

I would think yes, for the same reason you suggested, the current draw would not be enough.
Allan Reeling

Hazard flashers work on voltage not current, they are designed to flash at the same rate no matter how few bulbs are working, and for long periods i.e. battery running down i.e. current reducing in the aftermath of a collision.

The usual way of accommodating LED indicator bulbs is to add a ballast resistor each side so the current remains the same, therefore both flasher units should work as before. However that nullifies the 'bulb failure' feature of indicator flashers which lets you know if a corner has failed, as all it is doing is monitoring the current through the ballast. So unless you frequently check them you won't be aware a corner has failed, and neither with that truck bearing down on you when you are slowing for a turn.

There are LED flasher units, but you have to differentiate between those and the more common electronic flasher unit for incandescent bulbs. Whether those retain the 'corner failure' feature I don't know.

As for the hazards, because they work differnetly as above you may need to replace it or you may not, try it first. Some flashers units are said to be universal and will flash all incandescent, all LED or a mixture, and either indicators or hazards. At the end of the day you are dependant on the accuracy or otherwise of the descriptions in adverts.

Bob, I have fitted LED bulbs for my turn signals and I did also fit an electronic flasher unit (much louder than the old one). You need to fit two ballast resistors (one for each side) and the Hazard flashers will work ok with the existing Hazard flasher unit. See this link:

Fitting these ballast resistors will also enable you to use your old turn signal flasher as well (handy to have a spare).

Andy Robinson

You've lost me Paul. I've dismantled both turn and hazard units and they look largely the same. i.e. bi-metalic strip and heater.
I would advise anyone with a failed unit to buy solid state anyway, the modern bi-metal replacement efforts are dreadful, as are the 6RA's, by the way.
Allan Reeling

Whilst both use a heated bi-metallic strip, hazard flasher units should be open-circuit normally, indicator flasher units closed normally.

When you turn on the hazards there is a short delay then the corners start going on-off-on-off.

With indicators (except early Mk1 cars which use a different system) when you first operate the switch the corners should light up straight away - to give the earliest possible indication - then after a short delay start flashing off-on-off-on.

The same difference in construction is what allows the hazard flasher unit to operate anything from 1 to 4 at the correct rate, and very low battery voltage. Indicator flasher units will only flash correctly with two bulbs of the correct wattage, plus a side-marker and tell-tale, and with good voltage. It's why they are tested with the engine running, and hazards (I think) are checked with both engine running and not running.

I agree modern bi-metal replacement are poor. I rejected two replacements from the MGOC for an original I felt was a bit slow albeit still legal. Both were even slower, the second one not even legal. I carried on with my old one.

People replace them with a modern 3-pin electronic which aren't so susceptible to current as a way of dealing with poor connections - and there are many of them! However it needs to borne in mind that bad connections are contributing to dim flashers, and that will still be the case with incandescents and a modern electronic flasher.

It also needs to be borne in mind that external LED bulbs are a grey area, and while they won't be rejected at the MOT they might by your insurance company - mine did when I bothered to ask having bought some and discovered the following legend on the box: "Off-road use only".


Paul, Thanks for that. What I found with LED's was that you needed to buy the coloured variety, otherwise the lens (plastic outer) colour was bleached out by the white LED's.
Allan Reeling

A pal has had two sets of stop/tail but they both suffered from various problems of flickering when they shouldn't. One of then had an additional problem whereby if the tail lights were already on applying the brakes did not make them any brighter. The attached is the other set with stop and tail illuminated, and as well as noticeably less light directly back there is very little light to the sides. Stop lights in direct sunlight are -at best - no brighter.


Bob, Iím not sure why youíre looking to replace the flashers with LEDís, Iíve tried at a couple stop/tail bulbs and as Paul and others have mentioned the light output pattern and intensity left a lot to be desired. My personal suggestion would be to leave the bulbs as standard and just replace the flasher unit with an electronic version. This will give a nice constant flash rate, let you know when a bulb has failed and look original.

R.A Davis

LED bulbs effectiveness seems to be about which ones you buy and where from.

You can tell when good LED bulbs (of the correct colour) are fitted when compared with standard bulbs even when those standard bulbs are fitted in cleaned holders, reflectors, lenses (cleaned inside and out), connectors and wires.

See Part No. 2 - 12v 21w AMBER BA15s in link below, I've seen that they work well -

Nigel Atkins

Why bother going to all the trouble of converting flashers to led
It's not as though the current draw of normal globes is a problem and you won't go any faster or further on a tankfull of fuel
Why fix something that works ok anyway

William Revit

I don't think I'll be fitting LEDs any time soon.
Dave O'Neill 2

The only viable argument for changing from standard would be for increased visibility. But whether LEDs is the way to go is highly debatable.

See and be seen just a matter of increased safety. The be seen is more relevant to indicators and rear lights particularly the rear side/brake lights but also number plate lights - which is why I also like reflective number plates (that work off other sources of light too).

Why bother improving anything on the cars they all work (or should) OK.

Some prefer to polish the cars and/or add on more bright parts to make them more noticeable, each to their own.

Hazard lights that draw less from the battery might be useful when being used on a vehicle that's broken down as they'll flash brighter for longer which could improve visibility, if only for the recovery truck driver to see.

Certainly the BGT broken down last Thurday in Wellingborough needed brighter hazard lights - battery conditioner on passenger seat, batteries very flat and fuel problems - new owner(?), occasional user(?), typical PO(?), (typical classic car owner(?) bad luck(?).
Nigel Atkins

Out of interest and for the sake of a couple of quid I bought an LED flasher unit. Connected up to two LED units (actually the stop light part of stop/tail units) it just flashed once!

I found it needed more current to flash, even though the unit says it works with 0.02A to 20A, and the two 'bulbs' take 0.9A. An incandescent tell-tale boosted that to 1.2 amps and that was enough, but if you have LED tell-tales as well it isn't.

They come on instantly as they should i.e. not after a delay as with a conventional hazard flasher, but of course it has no 'corner failure' warning feature.

I don't know but, could a couple of quid LED flasher unit be too little to be of reasonable quality? You've put that it didn't work within its stated range.

IIRC the (non-LED) electronic flasher unit below showed up 'corner failure' by flashing faster same as the standard fitted flasher units do.

I'm only referring to indicators and not hazards.

Nigel Atkins

The 3-pin electronic indicator flasher for incandescent bulbs does indicate corner failure, by flashing at double-speed (although I've known some people not to notice that!).

You can pay up to £15 for an LED flasher, I'll let someone else try one of those :o) My point was that there is more to switching to LEDs than might at first appear. Not only are the LED units themselves very variable in how they perform but so are these flasher units.

Totally agree, as with many parts and suppliers it often pays to buy a full set from one reliable source rather than going for various sources and looking only at the least expensive.

Whilst the LEDs don't give warning of corner failing most/all(?) models of the car don't give warning of fails on other lights, particularly important for the rear lights. Faulty/intermittent brake light switches (some from new) are only picked up by vigilance or by others that are good enough to point this out to you.

Of course if the brake lights are bright enough you can often see if they're working just by looking in the rear view mirror.

Most lights I can check to see if they're working from the drivers seat at night but during daylight I have to call for the help of the very reluctant glamorous assistant.
Nigel Atkins

Many modern cars these days have an external bulb failure warning system, which maybe something to do with CAN-bus. But it seems that only works with incandescent bulbs as well. To fit LEDs you have to use load resistors or get a continual bulb failure warning, and some LED units contain these. Fair enough they will report failures up to the bulb connector, but not if the LED elements start failing. I've also seen someone recommend wiring in incandescent bulbs hidden away somewhere so LEDs can be used!

I've converted my stop/tail/indicator and side lights to LEDs for safety reasons. And I fitted the circuit for hazard warning lights.
I replaced both flashers and everything is working well.

Mike Christie

Except you will have lost the 'corner failure warning' feature, which is a safety feature ...

Maybe Paul,
But I've gained very bright stop/tail/indicators and front daylight running lights.
And since in England cars without daylight running lights are becoming 'invisible' to other road users, driving my 1968 MGBGT feels much safer.
Mike Christie

It's a matter of personal preference as to whether you stick with incandescent bulbs or change them for LED's. I have changed all my bulbs apart from headlights to LED's, including the instruments (much brighter). I also have used coloured LED's for the stop/tail and indicators to match the lens colour. As it says on the Moss website - " Pink is not the universal colour for stop Ē.

Certainly with indicators there is the disadvantage of having lost the "corner failure warning", but as Mike has said there are many advantages to changing to LED's from a safety perspective as they are definitely brighter and of course draw a lot less current than conventional bulbs. I also now have daylight running lights which is a great advantage on a small car on todays roads.

Andy Robinson

The trouble is there are LED lights and LED lights. A pal has had two sets and neither were satisfactory for various reasons. The second set aren't even as bright as incandescents, as posted and shown a fortnight ago.

I agree about DRLs, which I why I made some for the roadster. The headlights are on in the attached.


Although not strictly relevant, I have also changed my stop/tail/and indicator lights for LEDís on my í53 TD. The front side/indicator bulbs have an Ďelementí which flashes a bright orange when turning. And so I now have bright daylight running lights and indicator lights both front and back, which are very useful on motorways and driving in Europe.
Weíre off in the TD for the MGCC Switzerland Rally in August and I will feel much happier knowing I can be seen clearly.
Mike Christie

This thread was discussed between 15/04/2018 and 19/05/2018

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