MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Hazard Flasher Fault

Hi all,
I am throughly, enjoying the 1971 MGB-GT that I recently purchased. One of the things that needs attention is the Hazard lights. Only the drivers side (left side) front and rear lights are flashing at this time as well as the indicator on the console. All the turn signal lights blink when I use the turn signal stalk. (altough, that was not always the case) I had to take the fuse block out and clean all the contacts there because sometimes the right side front and rear turn signals were not working either. At one point I did get all four hazards to work. But not sure if it was something I did or it just began working on it's own. Only the left side is workig at this time. Tracing down electrical faults is my least favorite thing to do.

Does anyone have any suggestions as to where the most likely cause to the problem may be? I'm hoping this may just be a commonly known problem with a quick and easy fix. As I have other mechanical things I would like to concentrate on doing at the moment.

Thanks for your suggestions.

John Fraioli
1979 Inca Yellow Roadster
1971 Blue MGB-GT
John F

Hi John- Try reaching behind dash with flasher turned on and wiggle the connections at back of switch. Put pressure up and down side, etc., and watch the indicator light on dash to see if right side indicator blinks "on" during fiddle. I've found hazard switches produce symptoms you describe. If no luck, you are stuck with extracting bulbs, front and rear, cleaning with acid, steel wool, plumbers fitting brush, or whatever, and retrying. This is usually where these buggers foul out: at the bulb grounds! The 71 splittail is my favorite car I must say! Cheers, Vic
vem myers

Vic,
Thanks for the tip.

My BIG mistake. The car is a 1972 GT. I have had it less then a month now, it is so new to me I guess I just forgot what year I had. Or it could have just been a senior moment. Anyway the hazard switch is on the center console below where the radio is. I guess your advice would still be the same. I will loosen the console screws, slide it forward and try messing with the switch. Unless you have some other advice in this stiuation.
Thanks,
John.
John F

John- Its all prettymuch the same from 70-80 on the MGBs. You can download the schematics, and print them out. If you plan on having lunch frequently with the Prince of Darkness, take your printout, in color, to the nearest Kinkos and have them blow it to 11 x 18 then plastic coat it. I use erasable wall board markers to highlight the areas I'm working on. I think when you wiggle around the back hazard switch, you'll prolly get a stray click on the indicator light, and then either rebuild or replace the switch or acid/brush clean the connections. If not, move over to checking the flashers mounted on passide firewall. Cheers, Vic
vem myers

John; On your Hazard switch you will find 6 prongs. One set is a group of 4 and the remaining two are on the bottom. When your Hazard switch is in the off position the two bottom posts are supposed to be connected together, They are both green. When connected they supply power for the direction lights. Just put a jumper on those two and then follow the power to your problem. Most likely just corrosion in the connector plugs and light sockets.
Sandy
Sandy Sanders

Try Sandy's test with the green wires. If the lights work, it's probably the switch. See if you can get a used switch - the new ones from China fail fairly quickly. The used ones from parts cars come up on e-bay regularly.
...

It'll almost certainly be the switch itself, these are so little used the grease inside hardens and acts more as an insulator than a lubricant. The usual problem is insulating the connection between the two green wires when the switch is off, which disables the turn signals. When the switch is on the other four terminals should all be connected together, which are the two sides, the 12v supply via the flasher unit, and the additional tell-tale.

Try flipping the switch back and fore a few times. If that fixes it all well and good. If it only does for a while, or now there is some other problem, dismantle the switch in a poly bag (to catch the bits), dig out the old grease and put in some fresh.
Paul Hunt 2

Wiring diagrams are available at http://www.advanceautowire.com click on stock schematics.
Kimberly

Thanks for all the suggestions. Just to reiterate. All four of my turn signals are operating. When I flip the hazard switch to on, only the front and rear on the left side works.

I spent a lot of time over the weekend going over other areas of the car, so I did not do anything in regard to the Hazards.

Found that the battery connections were not real snug and dirty. (although the car has been starting with no problems. So I replaced the terminals there. The horn also does not work. The sterring wheel was not centered when the wheels are straigt. So I took the steering wheel off and looked at the horn mechanisms while in there. The archives were very helpfull in diagnosing the problem there. There is a part missing the clear tubular part with the brass ends and springs. While I was taking the steering wheel hub off, I did hear the horn honk a couple of times. But once I got into the column area I found the purple wire and pulled it off it's terminal and checked it for 12v and found no power to it. Put the steering wheel back on and was able to get it perfectly orientated to the wheels.

I also spent a lot of time cleaning out the bulbous end to the drain from the fresh air vent box. which was plugged with crud and leaves. Now the vent box drains well. It is suprising how many people don't know that that plugs up if you let leaves into the vent box. So I used a piece of screen under the vent grill to keep junk from getting into the box.

Thanks to eveyone,
I will keep you posted as to what I find with the hazard lights.

John
1979 Inca Yellow MGB
1972 Blue MGB-GT
John F.

Hazard lights are on a different circuit than the turn signals. Look at the wiring schematic for your car. The problem is most likely the hazard switch. Check the output of the hazard switch.
Kimberly

Hazard switch, hazard switch, hazard switch!

If you are talking about the 71 for the horn problem then it isn't a purple wire but a purple/black (the purple will be for the headlamp flasher). But having said that with the horn button *not* pushed you *should* see 12v on the purple/black, which will be coming up via the horns themselves. The horns have 12v connected to them from the purple circuit, and the horn button connects a ground to the purple/black to sound the horns. So no 12v on the purple/black means either there is no 12v reaching the horns, or the purple/black is broken between horns and horn button. So check for 12v on both horn terminals to see where to go next. And if the headlamp flasher and courtesy lights don't work either, then the problem (or the main one at least) is likely to be in the fusebox with the purple fuse. But if the horn honked when removing the wheel, the circuit is fine and it sounds like the button is the problem, in which case there *should* be 12v on the purple/black!

Paul Hunt 2

I'm with Paul - it's the switch. It's almost guaranteed. The are notorious for failing. Get a good used switch - that will fix your problem.
...

I also have a 1972 MGB, although mine is a roadster. The hazard switch is very simple and easy to disassemble, clean, and reassemble. The switch and bezzle come out together by squeezing the sides of the bezzel (it has clips molded in to hold it in place, two on each side, top and bottom). Follow Kimberly's advise and get the wiring diagram from advance auto wire. It is in color and will help you to keep the wires straight.

After removing the switch/bezzel assembly, the switch should be easily pulled out of the bezzel. You will need a small, flat blade screw driver to pry the switch assembly apart. Be careful! The switch contains small parts that you don't want to lose. Pay attention to how everything fits together.

There is an "I" shaped piece of copper inside the switch that you will want to clean carefully. It completes the circuit depending on which side of the switch is pressed. Also clean the contacts on the inside of the switch, and the spades on the outside of the switch. Be careful. The spades are difficult to repair/replace if you happen to break one off.

Reassemble the switch, press it into the bezzel, reconnect the wires per the wiring diagram, and test the switch before pressing the assembly back into the console. If the switch was your problem, it should work now. If this does not fix your problem, look somewhere other than the switch.

Good luck!
glq Greg

Thanks again everyone for all the useful tips.

Paul: Your imput is always helpful as you describe the steps very systematically. This makes it very easy to locate the problems. As for the Hazard I have not addressed that problem yet. I will soon. About the horn. It was indeed the purple/black wire that I did check for 12v up at the steering wheel. No power there.
So now I have checked and I do have 12v at both the purple wire connections on the horns themselves. However when I remove the the purple/black wire from the horn and check for 12v on the spade that the wire came off of there is no power there. (this is the case with both horns. So I am puzzled. I would have thought that if I have power to the horn on one spade I should be able to jump the other horn spade to ground and get the horm to sound. This is not happening. Could there be a fault inside the horns themselves?

glq Greg: Thanks for the tips, I am glad to know that The hazard switch can just pop out of the console. That will be easier the disassembling the entire area. I will try to pry the switch out and clean it up. I will let you all know what the results are.

Today, I am taking the car down and get an emission test. Hopefully, it will pass so I can get my permenant plates.

Thanks,
John
John F

When the horn is energised it moves a diaphragm which opens the contact which breaks the circuit which causes the diaphragm to fall back again etc., and the diaphragm flapping back and fore makes the sound we hear. If you hear a click each time you power and de-power the horn the contact is stuck shut. But with no 12v on the purple/black when there is power on the purple spade either the contact is corroded and stuck open, or the horn winding is open-circuit. Ordinarily I'd say that the likelyhood of this happening to both horns is slim to non-existent and the problem would more likely be in the 12v feed from the purple at the fusebox or the ground feed through the horn button, but if the car is new to you one could have failed years ago and the other more recently so both horns could well have similar faults. These horns are generally adjustable with screw and lock-nut which is set in the factory, you could try slackening the nut and twiddling the screw to see if that gets things working again, but return it to its original position. People are often tempted to fiddle with this screw to try and make them louder wne the problem is bad connections in the rest of the circuit. Monitoring the voltage on the purple and purple/black terminals I described earlier will reveal if this is also a problem, when you eventually get the horns working.
Paul Hunt 2

This thread was discussed between 21/04/2007 and 29/04/2007

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.