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MG MGB Technical - Flasher unit

I have rewired my car to use an aftermarket 2-pin flasher unit (for turning signals, if the word flasher is ambiguous).

I go from the battery positive to the flasher unit to an aftermarket three-way switch (left - off - right) to the lamps to ground.

The system works. But not all the time. It's the middle of the night here, and I suddenly started wondering if the flasher unit's case needs to be isolated from touching the car body.

Anyone know the answer to that? And have any other advice about why a simple system like the one described should have problems?
Daryl

Cant see that the case needs to be isolated, assuming it is the standard type where the current heats up the bi-metallic strip (or a few coils of wire) causing the circuit to break, cool and remake. I have had new flashers fail in a few days, so having checked all the connections, I'd be inclined to get another.

You could test the one you have by putting a pair of correct watt bulbs on the output terminal and the battery-'ve and touching the input flasher terminal to +'ve.

(or any other bulb that takes roughly the same current- in UK 2X21Watts, so about 4 amps-maybe a 55W headlight bulb would do tho the flash rate may be greater.
HTH Michael
Michael Beswick

AFAIK the case on neither 2-pin or aftermarket 3-pin needs to be insulated from the body *or* connected to the body. The originals were mounted in a spring-clip and so would have been at ground potential anyway, the 3-pin ditto and the third wire is taken to ground. Unless it is loose and waggling around an after-market 2-pin in a clip which just happened to be at ground potential, if being at ground potential were a problem, would simply not work, it wouldn't work sometimes and not others. If is *is* waggling around then as well as the possibility of the connections coming into contact with things they shouldn't, the movement could be causing intermittent connections.

The original 2-pin flasher is very susceptible to bad connections - a bit of extra resistance in the circuit will make the bulbs glow but not flash. Is this what is happening? Or is one or both of the bulbs not even glowing? Is the tell-tale on the dash glowing? Or isn't it connected? The answers to these questions will make it much easier to direct you to the likely cause.

And like Michael I have had a new flasher unit fail in a very short time.
Paul Hunt 2

Hi Paul,

They either don't glow at all, or they flash as they should. The flasher unit is somewhat "wiggly" as regards contact with the frame. I will go and detach it fully and see whether that helps.

Yes, these aftermarket flasher units seem to fail "early and often", even a so-called heavy-duty one. I've had that happen on two of my cars. If that's the problem, do we know of a source for a bulletproof flasher? Seems ridiculous.
Daryl

Well, I isolated the flasher from the frame, and they're working. Too soon to tell if for real. Thanks, all, for now.
Daryl

The aftermarket flasher I installed (solid-state voltage sensitive type) is a two-prong unit, and as the outer is made of plastic, there's no chassis grounding. It's been running perfectly for 8 months - are your turn signal earths & voltage delivery all good?
Curtis Walker

If neither side even glows when the fault is evident then the problem is almost certainly in the 12v supply to the unit, its connection to the switch, or the switch itself. Any problem closer to the lamp units than that will only affect one side, and grounding problems usually cause the lamps to switch between flashing normally and just glowing, unless the lamp units are actually loose in the body. Remember that the rear light units on all cars and the front units on chrome bumper cars ground through their physical mounting and not through a ground wire. Only the front units on a rubber bumper use a ground wire. Where the problem is with a light unit or the feed to it the symptom is that while the faulty unit may not light at all, the other unit glows but does not flash (but see below).

Beware of so-called heavy-duty flasher units, many are no more than hazard flashers, will flash with anything from 1 to 6 bulbs connected, and hence do not have the failure mode whereby the flashing rate changes if one of the bulbs has failed. With a proper turn flasher unit with one bulb failed the other one glows steadily in the case of the original 2-pin flasher units, or flashes at double-speed in the case of more modern 3-pin units.
Paul Hunt 2

I marvel and am humbled by the great diagnosis advice I find here. I ought to confess that I am at the MGB pages even though this car is a Bugeye, because I find the advice even better here than at Spridget hq!

As far as connections and grounds, I totally re-wired this car, using only soldered joints and new plugs, and I took all the grounds to just two locations that I can easily check on. I doubt I have a wiring problem, but never easy to totally rule out (except see later). The wiring is so generic now that it is pretty well car-type-independent.

I forgot to mention that the line contains a dashboard telltale light (small, pencil diameter), and that is part of the resistance in the circuit, the rest being two 1157 bulbs (one front, one rear).

As far as volts . . . maybe a bit of battery decline since installing the battery and not running the car . . .

But here's the good news. The Bugeye is only just complete, and what I was describing was a flasher problem right after initial fire-up. Since then, I've driven the car some miles (boosted the battery, no doubt), and also propelled electrons mercillessly along all the wires to shake loose the murphygrubs. The flashers have mostly worked, and I may not really have a problem now.

Thanks again.


Daryl

On my 67 gt I tied the line to the dash flashers and to the exterior flasher lights together and was able to use a generic 2 prong flasher, rather than some unique product. I am running a negative ground system.
Barry
Barry Parkinson

If you have wired a dash tell-tale *in series* with the flasher unit then a correct (lamp failure indicating) flasher unit wouldn't flash at all, it will just glow. Ditto unless you are using two 21W bulbs for the main lamps each side. If you are using an after-market type flasher with no bulb failure warning (the so-called 'heavy-duty flasher') then it may well tick but only the tell-tale will flash, it will limit the current so much the main bulbs probably won't glow at all.

If you only want one tell-tale then you can connect the one side of the bulb via two diodes to the two wires feeding the main lamps, and the other side of the tell-tale to ground.

But all that is by-the-by, if you say sometimes it works and sometimes it doesn't then you haven't given us all or the correct information on how things are wired, and you have a bad or open connection somewhere. I'll ask directly this time - when it *doesn't* work do the main lamps glow but not flash? Or don't they even glow? Do both sides fail or only one?
Paul Hunt 2

This particular flasher unit is "aftermarket" and it is not labeled heavyduty.

The one telltale is wired in series, and leads to the switch and to ground. The two bulb each side are type 1157 whose wattage is unknown to me.

The bulbs either flash, or there is no light at them or the telltale at all. The bulbs and telltale never are constantly on.

Initially the problem was exhibited on the right side. Later it occurred also on the left side but less often. Lately it has rarely been occurring at all.

Two other clues that point to battery. The wiring is through "ignition on" but initially it took a fired-up engine to make the flashers work at all either side, whereas now (after some car usage) they work with ignition on and a dead engine. The other clue is that they first worked on the right side after I unplugged and then plugged again the connector to the front right bulb, thus possibly improving the conductance through this connector that had had too high a resistance for the available juice.

Daryl

It's not uncommon for the flashers to *glow* but not flash with the ignition on but the engine off, also if the engine is running but there is a lot of electrical load on the system. This is caused by one or more bad connections through the system, usually more than one, which means there will be no single 'magic bullet' to get them working properly, and it takes time to work through the connections.

If you are saying that first one side doesn't glow at all but the other side flashes OK, then both sides don't glow at all, I'd say the problem is in the switch, particularly if the tell-tale isn't working either (although I still don't see how you have the tell-tale wired to flash for both sides, unless it is connected *between* the two sides and not to ground). Not glowing at all is relatively easy to find compared to 'glowing but not flashing', you just track 12v from the ignition through fuse, flasher unit and switch. And where it changes from showing 12v to showing nothing (or very much less than 12v) the fault is between those two points.
Paul Hunt 2

Paul,

Thanks. I need to leave this for a day or so. As of now, I don't think the bulbs ever glow constantly, but it might help to look after dark. My current impression: they both flash one side and are totally off on the other side; or they both flash both sides.

I will send you by email a wiring diagram which shows how it is possible to have a single telltale.

Daryl
Daryl

This thread was discussed between 30/03/2006 and 03/04/2006

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