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MG MGB Technical - hazard switch or flasher - the culprit?

Hello all,

Trying to troubleshoot a hazard lights problem on a 1980 MGB.

All of the signal lamps work, and I'm able to get the turn signals working just fine when the key is set to ignition. But, when I set the hazard lights rocker switch to on, either with the key in the ignition setting or completely off, I get no hazard flashers.

Does this sound like a switch or flasher unit problem? Any thoughts? Thanks in advance.
Kevin Shertz

It could feasibly be either.

The easy way to check is to remove the hazard flasher unit from the circuit and join the two wires together. Then when you turn on the hazard switch, all the indicator/turn signal lamps should be permanently on. If not, you need to check for 12v at the switch.

If you have 12v into the switch but not out of the switch, you have a faulty switch.
Dave O'Neill 2

Thanks, Dave, for your prompt input. I'll check the flasher unit tomorrow -- don't look forward to having to get to it, though! -- and report back what I learn.
Kevin Shertz

It is as Dave said. The two wires that you need are both green. They are on the bottom of the switch seperate from the other four wires. When joined together they supply power to the flasher relay and flas all four lights.
Sandy
SANDY SANDERS

Could be either as Dave as said, the in-line fuse feeding them, or wiring around any of those components.

The two green wires supply power to the *turn* flasher unit when the hazard switch is *off*, not to the hazard flasher. Green wires are fused ignition, whereas of course the hazards are available at all times.

Brown (unfused always on) feeds an in-line fuse (usually behind the centre console and very convenient!) but confusingly stays brown on the other side. This goes to the B terminal on the hazard flasher, so perhaps the first thing is to check you have 12v here with a meter or test-lamp. Light-green/brown comes off the L terminal of the flasher unit and goes to the hazard switch. With the hazard switch on this wire is connected to the green/red and green/white flasher bulb wires, and also to a light-green/purple which lights a repeater lamp on the console if you have one.

Unlike the indicator/turn flasher which is effectively 'switched on' initially so the lamps light the instant you operate the switch, the hazard flasher works the other way round and is 'off' initially, and the hazard lights will only come on a second or so after operating the switch. This means that with the indicator flasher you have a low resistance path to 12v which will be seen by a meter or a test-lamp, but neither will be enough to start it flashing. The hazard flasher has a high impedance path to 12v, which a conventional test meter should 'see', but a test-lamp may not. A meter will definitely not start it flashing but a test-lamp may, even though the test-lamp itself isn't initially lit.
Paul Hunt

Followup: I checked both the flasher unit and the flasher switch - the switch seems to be the culprit.

When I was wiggling it in the back of the dash, I was able to briefly get it all to work properly. Disassembling and re-assembling the switch several times to clean the contacts enabled me to get flashers on one side of the car but not the other, and the plug/wiring all seems sound, so I've just ordered a new switch.

Thanks again for the help... and Paul, thanks so much for your detailed info regarding the wiring. Now that I have the dash area disassembled for checking the flasher unit, I'll have to see if I can locate that in-line fuse you mention for future reference!
Kevin Shertz

Mine was intermittent when I got my V8 15 years ago, but the indicators not the hazards. Flipping the switch back and fore a few times got them to work - briefly. So I dismantled the switch in a poly bag (to catch all the bits), dug out the old grease which had hardened and put fresh back in. Been fine ever since.

Since then I've tried to repair one of the later illuminated rockers but they seem just a bit too small and delicate for reliable results, with my fingers anyway.
Paul Hunt

New switch arrived, is now installed, and has fixed my flasher problem entirely. Huzzah! Thanks to all for your guidance and insight.
Kevin Shertz

This thread was discussed between 06/10/2009 and 09/10/2009

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