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MG MGA - Hazard Switch

Hi folks
I have been given a NOS Lucas 155SA hazard warning switch (see pic),the only drawback is-no wiring instructions.As far as I can work out,Black-earth, Purple-12v inline fused supply,Green/white-RH front & rear indicators,Green/red-LH front & rear indicators, which leaves two Green/brown wires.Do I disconnect the green wire from the B terminal on the original flasher unit on the car & attach to one Green/brown from the hazard switch then attach the other Green/brown back on to terminal B, thus routing the power from A4 on the fuse unit through the hazard switch?. Help required (I don't want to set fire to anything)
Sorry this is a bit long winded, but I cant think of any other way to explain what I wanted to say!
Steve Ash

S Ash

1500 or 1600?
dominic clancy

1622.The hazard switch is supposedly universal.
Steve A.
S Ash

If you are electrically able, you might be able to "infer" the wiring from these 1500 wiring instructions.
Chuck Schaefer

From the Mini Cooper Register website:

I too have one, a 54006501, which I was going to fit to a proper Mini, and never got around to.

It does have the instructions dated 1970 but, regrettably I have no scanner.

The first page says basically what it is.

The next page, and the important bit says

1) Connect the black cable to a convenient earth point on the vehicle body. If the Hazard Device bracket is screwed to a metal facia, the Black cable, with a small eyelet soldered to it, can be earthed through one of the fixing screws. It is essential to remove any paint so that a good metal to metal contact is made between bracket and panel.

2) Connect the Purple cable to a convenient battery supply point (such as the ammeter, feed side of the ignition switch, or the headlamp flasher feed point at the steering column).

3) Connect the Green/White cable from the Hazard Device, to the Green/White cable in the existing R.H flasher circuit. This can be done at the point where snap-connectors join the panel harness, to the main or bulk-head harness (the snap-connectors referred to can usually be found on most cars, behind, and to the right-hand side of the steering column.

4) Connect Green/Red cable from the device to Green/Red in the existing L.H flasher lamp circuit, in the same manner as (3) above.

5) Disconnect the Green terminal from terminal 'B' on the normal FL5 flasher unit, and connect it to one of the Green/Brown cables from the hazard unit switch.

6) Connect the other Green/Brown cable to terminal 'B' on the FL5 flasher unit.

Finally, check that Hazard System will work correctly by operating the switch. Both front and rear flashing lamps on the vehicle, plus repeater lamps (if fitted), should flash simultaneously.

The back page just details how to wire up the unit if it is going to be fitted to an articulated vehicle or for use towing a caravan or trailer.

Good luck
A warning, the above probably assumes negative earth.

Malcolm Asquith

For an MGA it might only work on the 1600 model where front and rear turn signals are constantly connected together without the relay in between. Might be a no-go for the 1500 model.
Barney Gaylord

This has nothing to do with pos/neg earth, makes no difference.
And, it should work fine on a 1500, as you are just feeding power from the Haz switch to where it would normally be fed by the TS switch. That's one wire per side going to the relay, which in fact connects the front & rear TS together so long as the brakes aren't applied. Of course, the rear lights would not flash on Haz if the brakes were applied, but that is not a usual situation.

Fletcher R Millmore

I'd have to look at the switch circuit in that case. The standard turn signal flasher unit will only operate two lamps. With one lamp it won't flash. With three lamps it makes a substantially shorter blink at longer interval. With four lamps it might make one very short blink, then stay off for a long time before the next short blink. Otherwise it might sort of go nuts with a very rapid but weak flash, not good for 4-ways at all. That's why newer cars have two flasher units.

I thought this switch had the extra wires to switch in a separate heavy duty flasher unit to handle four lamps at once (and switch out the original flasher in the process). If it was only connecting L&R switch terminals at the same time it wouldn't need that many wires.

When I installed 4-ways on my MGA 1500 I did connect L&R signals at the same time. I also changed the standard flasher unit to a heavy duty unit capable of working 1 to 6 bulbs at a constant flash rate. This handles my trailer lights at the same time (when connected). However, with the HD flasher there is no cockpit warning if one bulb burns out, so you have to be vigilant about checking turn signal lamps very often.
Barney Gaylord

Cute. There is currently on eBay a Lucas 155sa switch that has only three wires (and a plastic connector). Here's mud in your eye:
Barney Gaylord

Barney -
My understanding from the wiring description is that this switch has the Haz flasher incorporated in it; remember that this was a standalone retrofit unit. The GN wires bypass the normal flasher when the Haz function is activated, just like on all standard Haz installations.

Fletcher R Millmore

Okay, I got it. Malcolm's directions are correct for the 6-wire switch to be used on 1959 and later type circuit with no relay unit where front and rear turn lamps are common (connected together). This should be suitable for Steve's switch when used on the MGA 1600 model.

To be use on the 1500 model with separate front & rear lamp circuits and the relay unit, two more wires need to be added to the switch, following the instructions.

The output of this switch is a 4-pole normally open switch. When switched on it connects the internal flasher output to all four wires for the four corner lamps (only 2 needed for the 1600 car). On the other side are two wires (Green/Brown) connected to a normally closed switch. When switched on this contact opens to disconnect power from the original flasher unit (so the two flasher units don't fight each other). The other wires are power (always hot) for the new internal flasher unit, and ground for the internal indicator lamp (lighting up the knob).

It will be fun drawing the internal schematic of this switch including flasher unit and pilot lamp. Maybe next week. I'm off to GT-35 for in a few hours. Nice to live only two hours away from Delavan.
Barney Gaylord

This hazard switch has a built in Lucas 9FL 12v 12A flasher (35053A)

Steve A.
S Ash

There are a couple of old ones and a new repro on eBay UK if anyone is interested!

This thread is very interesting as I have an original unit for my Mk2 Jag that I always intended to fit, now I have the missing instructions!
Neil McGurk

This thread was discussed between 26/07/2010 and 27/07/2010

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