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MG MGB Technical - Hazard warning flasher not flashing

In my newly acquired 74 B the hazard warning lights do not flash but simply stay illuminated. The turn signals, however, to flash OK. Am I correct in concluding that I simply (famous last words) need to replace the flasher unit for the hazard warning lights?
H Wallis

Hi H Wallis, welcome,
best never assume especially with an old car new to you.

All cables, wires, connections, switches want to be clean, secure and protected.

Hazards are rarely used so it may just be a case of the switch needs a bit of exercise to clean the contacts. Always worth a try as it's free and easy to try. Disconnect the battery(s) push the switch on and off a couple of dozen of times.

Then there's poor connections at switch or flasher or the wires to the connectors.

Also possible is that the the hazard switch and/or unit are wired incorrectly.

Two really useful pieces of info for you - many modern made parts are of piss poor quality because many classic vehicle owners are tight-fisted and insist on the very cheapest parts they can get as they rare use their vehicles. This AFAIK includes modern made flasher units, the original units last many decades (do they ever break(?)) I'd get a working s/h one if I ever had to.

Second, if you've not already got a copy then get yourself a relevant copy of the Driver's Handbook that would have come with the car when it was new (which will include a wiring diagram) and if you read it and refer to it as required it will lots that you need to know and by reading it you will know more than many long term owners of the car.

Example (of combination reprint) from mine for my Midget. - https://www.brooklandsbooks.co.uk/product-category/a-z-cars/mg/owners-handbooks-mg/

Paul Hunt's excellent website is also full of info. - http://www.mgb-stuff.org.uk/hammertext.htm

Let us know how you get on.





Nigel Atkins

Sorry I forgot to put -

Could be poor earth(s) to the lights themselves, or their combined units, which only shows up on fuller load.

Without the engine running, try turning on all side lights and main beam, reverse too, foot on brake pedal to get them on too, then turn on the indicator one side and check all lights for brightness and any cross dropping, then try the other indicator side.

Again all free and easy to check.

This also highlights that you always want the good quality battery(ies) in good state of charge with all the connections and cables (earths) in good condition and clean, secure and protected.

This is particularly so when the car is new to you and/or you're looking for electrical or engine starting problems - not that you'll have any, well many. 🙂

Nigel Atkins

Unlikely to be earths to the lamps, as the indicators (turn signals) are working, and they need full current flow in order to flash. The hazards, on the other hand, are less load dependent.
Dave O'Neill 2

Thanks for all the suggestions. Will certainly look into them. Car is generally in very good condition and, after I figured out the wiring to the alternator, which had not been properly re-connected after having had an engine seal replaced before I took delivery, most electric and "battery failing to charge" issues went away - just this one left at the moment.

I was careful not to use the word "assume" in my original post - you will notice I said "conclude" instead. Always careful to avoid that accusation LOL.
H Wallis

Dave,
I bow to your superior knowledge but on a car new to owner a check of all lights under load wouldn't be a bad idea as I've seen weird and intermittent stuff and effects with PO wiring.

And Jan started with an issue with IIRC his front indicator and then had another electrical lighting issue, they can be isolated issues but often the same age, use/abuse applies to similar parts and components.

I was expecting Paul to come in and tell me off for wasting time checking other stuff instead of solving just the issue presented. 😊


Nigel Atkins

H,
you may correctly conclude that I don't always read the posts correctly and answer correctly (even if I've read the post correctly). 😊

I always recommend carrying out a full 36k-mile service check in stages in-between driving the car to get used to it and discover and iron out any wrinkles and discover how well it could or should go.

Obviously all work and testing must be followed with a good long road test - it' the law! 😀
Nigel Atkins

H,
see attached as a representation (do check in the relevant Driver's Handbook wiring diagram).

As you can see the hazard has an independent supply that should keep going, well as long as the battery(ies) last - but to my surprise it is fused so that may be the answer, of course you need to know what caused the failure of the fuse but with previous wiring being wrong perhaps just an error by someone.


Nigel Atkins

To your first post, almost certainly 'yes'. Current has to flow through the hazard flasher to reach the switch, and if all four lamps are lighting when that is on, and the indicators work correctly when it is off, then there is a very good chance the connections are correct and good including in the switch.

As the car is new to you it may simply be that the PO bypassed the flasher unit for some reason i.e. it's not in circuit, as these rarely fail, or an incorrect unit of some type.

Have you located it? It should have a brown wire one side and a light-green/brown the other. The indicator flasher has green and light-green/brown, but you will be able to identify that from the clicking when they are on.
paulh4

With PO wiring and/or piss poor modern made parts I've seen some weird stuff happen, plus some of the posts and photos on the BBS, which can make things difficult to conclude from.

Although of course it could be the rare and sometimes obvious of the original (or more likely replacement) gone bad.

Be a strange idea to bypass the flasher, but always possible, could it be the wrong flasher fitted that has enough to make the connection but not break it(?).
Nigel Atkins

OK - thanks all - sounds like I am going to have to remove the centre console to check all these so I will wait until I have a few more things lined up that need it to be removed. I want to install a different radio (to be kindly supplied by my brother-in-law) from what is there now (but doesn't work) and to fix the cigar lighter, which appears very rusty, so I have a convenient 12v outlet for 21st century equipment LOL.
H Wallis

If you remove the non-working radio you might be able to at least see what sort of hazard flasher unit you have and what wiring goes to it, though I've no idea if you'd be able to get at it through the radio aperture.

Removing the radio may also let you see that everything to the radio and behind it is standard and/or correct.

Perhaps the existing radio and cigar lighter just need the wiring sorting out which may, or may not, also relate to the hazard flasher unit.

Let us know how you get on.
Nigel Atkins

Last month I changed my hazard switch which was a straightforward swop. Plug out plug in. But the wiring was standard and not "butchered". Last year, I changed the clock and cigarette lighter by removing radio, unscrewing centre consul and gear lever ring. It's all doable unless you've got big hands!
Craig M Harvey

I think the ease with which you can do things is very much dependent on which model you have. Late rubber-bumper models are more awkward, and US models, with their different dashboards and centre consoles, could be different again.
Dave O'Neill 2

When first provided in the UK at least (1974) it was clipped to the right-hand upright below the radio, with an in-line fuse nearby. What a brilliant idea that was. By comparison those other items mentioned are 'easy', but the North American dash and centre console is very different.

Edit: Near-simultaneous post. However 'later' models possibly 77 and later have both flasher units side by side where the indicator flasher usually was.
paulh4

This thread was discussed between 17/08/2021 and 20/08/2021

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