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MG MGB Technical - Hazard warning light failure

Some ideas much appreciated; I have a UK 1972 BGT.

Today one of the small rear licence plate lights failed at the same time as the hazard warning lights no longer work when you pull the small red knob out on the centre console.

I have checked the bulb in the rear licence plate holder and the four fuses within the engine bay and all OK

Thanks for any help.
JP Mitchell

Check for poor connections in the trunk. I just went through the same thing and wound up replacing the bulb only to find out that it wasn't the cause of the problem. These cars are now over forty years old and some corrosion, at the electrical connections, is to be expected. RAY
rjm RAY

Thanks Ray,.....will have a look there and report back.
JP Mitchell

Hazards are not factory on a 72, so it depends how they were wired by whoever fitted it. Completely dead I take it, i.e. not a case of lights glowing but not flashing? It sounds like it is a composite unit with switch and flasher unit, so other than checking there is voltage going in from what should be a fused 'always on' source there isn't much more you can do. I take it the indicators still work when the hazards are off, hazards are supposed to disconnect them when on for safety reasons.

The number plate lights are fused with the parking lights, one fuse per side. If the front and rear lights are OK it's not the fuse or the connections to the back of the car. That leaves:

1. The red tail from the light unit that should have a single bullet connector close by, then a red wire in the rear harness that goes to the rear light cluster on the same side.

2. The light holder connections.

3. The earthing of the light unit. This is notoriously iffy on chrome bumper cars, having to go through the light unit, the overider, the bumper, the bumper springs, and the bumper irons before it gets to the body. When restoring mine I had to provide an earth wire, obviously the paint was too good.
Paul Hunt

Hello Paul,

Many thanks for your help.

I have had the car from new (!) and believe the hazards were fitted when I took delivery. This is the first time I have had a problem with them.

When the small red knob is pulled out, the hazards do light up but do not flash. I had the car rewired a couple of years ago, so will follow your advice and go back to the person who wired everything up.

The licence plate light is fine now. I had checked the rear wiring as recommended by Roy (above) but missed the loose wire the first time I looked. Now all fine.

Many thanks once again.

John M
JP Mitchell

I find it surprising that hazards would have been dealer-fitted to a UK-spec car in 1972, the first standard only appeared in 1965. You would have had to have requested it (or possibly got a car someone else had specced but not taken), if such a kit were available, which is what the pull-knob implies. That's on UK cars, US cars had them from 67, but operated from a rocker switch on the centre console with the flasher unit fitted elsewhere. If yours light but don't flash it sounds like the flasher unit has failed. Ordinarily hazard flashers (as opposed to indicator flashers) only light the lamps a short time after the switch is operated. If yours light immediately then it could be that the hazard flasher contact has stuck closed, so a sharp knock to the flasher might release it. But it will probably stick again, and non-working hazards are an MOT failure regardless of whether they were original fitment or an after-market add-on.
Paul Hunt

My '67 B had the wiring and connectors for the hazard switch when I purchased the car in '72, even though it wasn't available as an option that year. It became standard fitment on NA Bs in '68. I located a switch and subharness from a '68 parts car and it simply plugged in to my stock wiring harness giving me hazard lights at a very reasonable price with easy installation. RAY
rjm RAY

This thread was discussed between 09/09/2013 and 12/09/2013

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