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MG MGB Technical - Flasher Units

Hi all,

I just got two new flasher units from MG Owners Club, one 'normal' and one hazard. Now the two units have come but how do I know which is which?

One says

Wagner Flasher 223-12 volts

and the other says

Wagner 552 12 volts.

They are seemingly US parts: anyone over that side of the pond know which is which?

There are also no indication as to which of the prongs is which. Does it matter how they are connected?

Thanks in advance.

Andrew
Andrew H

Shouldn't matter which way round they are connected although I believe the original turn flashers were marked B for battery (i.e. green wire) and L for lights (light-green/brown). The hazard flasher uses brown and light-green/brown wires.

The turn flasher will go at double-speed if used in the hazard position, it may also be burnt out by using it like this for too long. I think I am right in saying that the turn signals light immediately the switch is operated whereas the hazard flasher only lights the lamps after a delay. So try each flasher in the turn signal position first.
Paul Hunt

# 552 is for the turn signals the # 223 is for the hazzard lights - I run an auto parts whse. , that is how I know .

-Nate
Nate

No offense, Nate, but a 552 flasher is not a turn signal flasher, even though it clearly states on the package that it is. In fact, it is a hazard flasher. The labeling on most 552 packs calls it a "heavy duty" turn signal flasher, intended for variable loads of 2 - 6 bulbs. On some packages, they even warn you that you won't get an indication of a failed bulb if you use a 552 for turn signals. By definition, that is a hazard flasher. What's the difference? I have copied below an excerpt from an electrical repair manual I wrote for Triumphs:
************************************************
TURN SIGNAL FLASHERS VERSUS HAZARD FLASHERS

Even though they serve identical functions, and they both operate on the same principle, there is a significant difference in the two. Each has a heat element and a bimetal strip. Current through the heat element elevates the temperature of the bimetal strip, causing it to bend. On one end of the strip is a set of contacts. When the strip bends, these contacts either open (turn signal flasher) or close (hazard flasher). The current that flows through the heat element also flows through the light bulbs.

Functionally, the differences between the two types are:

1) A hazard flasher will flash at the same rate regardless of the load, as long as the load doesn't exceed the flasher capacity. One 2 watt bulb will cause the flasher to operate at the same rate as four 21 watt bulbs.
The flash rate of a turn signal flasher will vary, depending on the load. The current through one 21 watt bulb is not enough to cause the flasher to work (the lights will stay on), and four 21 watt bulbs will cause the flasher to operate at a high rate (till the flasher burns up).

There is an excellent reason for this difference, and it is not unique to Lucas -- most manufacturers do this. The reason is one of safety. If you turn on your turn signal flashers and one bulb is out, the flasher won't work, giving you notification that something needs to be fixed. On the other hand, when you need to use your hazard flasher, you need to use whatever bulbs you have. If one is out, you still want to be able to use the other three. You won't have any indication that a bulb is out, but the next time you use the turn signals, you will.

2) The flash sequence of a hazard flasher starts with an OFF, i.e., OFF--ON--OFF--ON. The flash sequence of a turn signal flasher starts with an ON, i.e., ON--OFF--ON--OFF. This difference in sequence was not a design goal, it just worked out that way.
*************************************************

You can use a hazard flasher for turn signals (in fact, this can often be a quick fix - temporary - for turn signal problems) but you don't want to use a turn signal flasher for the hazard circuit, for the reasons Paul gave.

Paul is correct in saying that it shouldn't make any difference which way round you wire the units, and I have found this to be true on 552s. However, from experience I have found that on some Lucas units used on Triumphs it does make a difference. I have dissasembled a few to try to find out why, but I could find no reason for this. Never-the-less, I have had a few that would only work if wired the right way. Others (same part #) would work either way. Who can figure? They are Lucas, after all.
Dan Masters

Just to add to what Dan has said about bulb failure notification. The turn flashers used in our era of cars used the 'light but no flash' mode to signify a blown bulb. However this makes the turn flasher very sensitive to current, and many owners of 30 year old cars have problems of slow or non flashing under varying conditions. Rather than investigate and fix the real problems, which can be several and varied, some people choose to use an after-market turn flasher instead. Where these are the 'heavy duty 2 to 6 bulb' type you no longer know from inside the car that one of your bulbs has failed, and that 18-wheeler bearing down on you doesn't know you are going to stop and turn across the traffic. Modern turn flasher units work differently and flash at double-speed if one bulb is out, and if you really *must* do a frig rather than fix the real problem, this is the only safe kind to use. They may be three terminal devices instead of the two-terminal our cars are wired for, but for at least one I know of the third terminal is for a ground.
Paul Hunt

This thread was discussed between 05/09/2002 and 07/09/2002

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