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MG MGB Technical - Turn signal

I think my turn signal does not work correctly because of the flasher can. It is a "550" 3 pronged deal. I bought another 550 and it does not work at all. It there any difference between the modern turn signal flasher can and the old ones?
Frank Baker

Frank, the flasher for turn signals is behind the glove compartment. The flasher for the emergency lights is behind the radio. I've embarrassed myself a few times by replacing the wrong flasher. I think the flasher cubes are the same although some cars require a "heavy duty". The flasher you're using might just be the heavy duty. I was thinking the regular was a 502.
I'm in Greeley. What part of Colorado are you in?
Ken Thompson
1974 mgb roadster
Kenneth Thompson

What year car? The MGBs up to 64 did use a 3-pin flasher, but it is completely different to the modern 3-pin, but can be made to work with some wiring changes. From 65 on a 2-pin was used with different wiring, the modern 3-pin can operate these as is, the 3rd pin going to ground as in modern cars.

But the 550 seems to be for flashing anything from 1 to 4 27 watt bulbs i.e. it is a hazard flasher and not a turn signal flasher. Using a hazard flasher for turn signals is in itself a hazard as you won't know when one of your bulbs has failed, and that truck bearing down on you won't know you are intending to turn.

Turn signal flashers are designed to operate two lamps only, just glowing and not flashing (original thermal style) if one bulb fails, or flashing at double speed (modern electronic 3-pin type) if a bulb fails. Running more than 2 bulbs (apart from repeaters) from the thermal type will burn them out.

There is also reputed to be a more recent electronic type for low-current LED turn signals, but these are also damaged if used with more than one incandescent bulb, and I don't think they have the bulb failure warning either. You might say that multi-element LED units are unlikely to fail totally and so don't need the warning, which may be true, but the connections to them can fail which has the same result.
Paul Hunt 2

This thread was discussed between 07/08/2007 and 09/08/2007

MG MGB Technical index

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