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 - Funky turn signals

Ah.....the little challenges never end!!

Yesterday my turn signals suddenly started failing intermittantly on my 73B roadster. Three out of 4 times they work.....and then suddenly at the next corner they don't. Rotating the wheel doesn't help. However, once the turn is made and I'm driving straight again they always immediately work again. The trip back C-clip seems to be fixed in its proper location as the trip off occurs where it should in left and right turns.

When the signals fail it is both left and right that won't work. My backup and tail lights still work during the signal failure so it's not a fuse issue (assuming no buffoon has changed the wiring prior to my getting the car).

My thinking is to go into the switch, which I had out and dismantled and cleaned last year.

I'm having a hard time deciphering my nice color coded wiring diagram though. Can anyone tell me which wire is the 12v+ feed to the turn signal switch? There are a number of wires doing various things going in and out of the switch. I assume one of them is bringing power to the switch that is then routed through the switch to the left or right signal bulbs.

Thanks,
BH
BH Davis

HI there BH.


I had to look in the ole' Haynes manual for this one. Your switch on your steering column has three functions signal lights, high beam flash and High beam lock. As you probably all ready know. The main feed wire to your switch is a LGB wire (light Green wire with brown tracer)which comes from the hazard switch plug. The main wire that feeds Both the hazards and the indicator switch is a solid green wire that is connected to the fuse box and the flasher relay. And this also wire runs into a group of green wires.


OK, lets get to the point. Your hazard switch works a complete circuit for the signal lights and hazards to work. If the hazard switch is not hooked up or the contacts in hazard switch are corroded or bent the signal lights and hazards will work and short out.


At the age these cars are at I would recommend replacing both the Hazard switch and signal switch to cure your problem. But I should not preach to You what I have not done myself LOL.


BH, Make sure the wire plug on the back of the hazard switch is plugged in tight. And the wires at the relays (both hazard and signal) are plugged in tight. I would say rock the hazard switch up and down but that might not help here. hope this helps....



James D.

James D

BH-
Who published the wiring diagram you are using?
It is easy to enlarge and print just a section of the wiring diagrams available at http://www.advanceautowire.com
Make yourself an extra copy and use a hi-lighter to trace the circuit from the turn signal switch to make it easier to follow and not be confused with the other lines on the diagram.
Use a multimeter to test each connection for high resistance.
Kimberly

Thanks all.

I've got the Prospero's Garage 11x17 diagram. Very good and easy to follow the wire trace. There is just so much going on as you trace the wires in and out of the switch that I didn't find the feed going through the hazard warning switch.

Now that I know where to look I see fuse 3 (1 from the bottom of the block) leads a dark green wire to the hazard warning switch. From there I see the light green/brown wire going into the flasher unit, and the same going out of the flasher unit to the turn signal switch.

Thank you both for your help! This is exactly what I needed. Another half hour or so of tracing colored lines might have solved it but you made it much easier.

BH
BH Davis

That fuse feeds all the fused ignition circuits i.e. including the tach and electric gauges, so if they still work when the turn signals don't it isn't the fuse. The most common cause of failure of both sides is the hazard switch. This is usually so rarely used the grease hardens and becomes an insulator. Sometimes flipping the switch back and fore a few times can help, sometimes you have to dismantle the old switch (in a poly bag to catch the bits), clean out the old grease and put in some new. Hwever that is with the older non-illuminated rockers, I tried cleaning and tweaking an illuminated one several times but it remained unreliable so had to fit a new one.
Paul Hunt 2

Paul,

Turns signals went dead again today. They were out for about 30 minutes of driving. I got home and pulled the car in the garage and turned it off. Then I turned it back on the the turn signals worked.

When they were dead this time I checked the hazard lights and they still work correctly ........blinking all for lights and the dash indicators.

I followed the wiring diagram through and see there is a separate flasher for the hazard lights. The power for the turn signals goes out of the hazard switch and into the turn signal flasher unit and then on to the turn signal column stalk.

I know you said you think it's probably the hazard switch but what do you think about this business of the signals working again after the car is turned off and on. It makes me think of the possibiility of something going on the in the flasher unit. I suspect it works like a capacitor. If that is correct it could be failing after charge buildup and not letting any current through. Then on turning off the car it discharges / recharges and works until the capacitor reaches a failure state again. Sound logical?

Thanks,
BH
BH Davis

It could possibly be an intermittent flasher unit, although it doesn't work like a capacitor.

Next time it happens, remove the two wires from the flasher unit and join them together, then see if the indicators come on. They won't flash, obviously, but it will prove whether it is the flasher unit or not.
Dave O'Neill 2

Where is the flasher unit? I think I've heard that it is, or seen it, below the glove box (left hand US drive car). Is that correct?

In other words, pull the glove box or dust skirt below the glove box, to get at it?

Thanks,
BH
BH Davis

Yes the flasher is located behind the glove box. You may also want to clean all the connections in the circuit. Corroded connectors are a major source of eletrical gremlins.
John H

Go to http://www.advanceautowire.com click on stock schematics. You will find color wiring diagrams there. They're easy to print and the nice thing is you can use a hi-lighter to trace the circuit. You can also enlarge and print the part of the diagram you need.
Use a multimeter to test the resistance of each connection. As a connection gets hot, the resistance can increase.
Kimberly

Kimberly,

THANK YOU !!!! Great wiring diagrams. Much easier to follow then the actual wire path style of the one I already have.

Regards,
BH Davis
BH Davis

Locate the flasher unit by turning them on :o) Of course, this only works when they are working!

If the dash tell-tales weren't coming on when you operated the turn switch that implies an intermittent connection from the green feed, through the hazard switch, the turn flasher unit, and turn switch, and the connectors at the bottom of the steering column. If, when they are not working, you bypass the turn flasher and they glow, and are still not working when you reconnect the flasher, that does imply the turn flasher or its connections are faulty. But if it is the turn flasher you are just as likely to disturb the fault, and when you try them again and they work OK you will be no further forward. The Law of Sod dictates that an intermittent connection is likely to be intermittent during your tests anyway. With problems like this I have in the past rigged up a small voltmeter to various points in the circuit so I can monitor what is happening when the fault occurs (i.e. before it and during it), and track them down that way.
Paul Hunt 2

Thanks everyone. I have a new flasher and hazard switch in hand and will do the testing to see where the problem lies this weekend. I'm sure it shouldn't be too be a deal to resolve the problem!

Thanks again,
BH
BH Davis

Well, had it apart and took a look. Someone had run a new green lead wire from the instrument voltage stabilizer (below left of steering wheel) to the input on the turn signal flasher unit. I think they did this because there had been problems at the hazard switch connection sending power to the turn signal flasher. The original green lead wire was still hanging there by the flasher and was live so I just pulled out the scabbed wire and replaced it with the original.

At this point it's working fine. I'll give it some time to see if it continues to work.

I did determine that there was NO POWER coming in on the scabbed lead intermittantly but don't know why. Does anyone thing I should replace the instrument voltage stabalizer?

Thanks,
BH
BH Davis

Is the voltage stabilizer bad? Are you having trouble with the gauges? The extra wire you removed may have had bad terminals, corroded terminals.
Kimberly

Which side of the stabiliser was the wire connected to?
Dave O'Neill 2

No, the guages are working fine. I don't know what impact the voltage stabilizer is supposed to have so I can't say that it is or isn't affecting their operation.....other then if they were not working properly if it were bad then it must be fine.

The scabbed wire was the second from the end....but which end of course. Without taking the drivers side dust skirt back off I can only say that it was send from the end close to the steering wheel (US Left hand drive). From Moss sketches it looks like second from the other end has a female spade connector while all the others are male as one would expect. I'm pretty sure the scabbed on wire went on a standard male terminal.

If needed I can drop the skirt again and take a closer look.

Thanks,
BH
BH Davis

To check the voltage stabiliser just connect a voltmeter (or test-lamp) to the light-green/green output terminal. The original stabiliser turns 12v on and off about oncer per second, once the ignition has been on for a few seconds, so this is what you should see. However some people have replaced the original with a solid-state type which gives a constant 9 or 10v output, so you would need a voltmeter to confirm this. If the original type is giving a constant output clean and check its ground connection (mounting screw).
Paul Hunt 2

Thanks Paul. I'll do the voltage test next time I drop the dust skirt.

Much appreciated.
BH
BH Davis

Paul,

Light green/green wire teminal outputs 12v about once each second as you described. Looks like no damage was done to the stabilizer by the scabbed output.

Thanks again for your time, guidance and help!
BH
BH Davis

This thread was discussed between 15/07/2007 and 25/07/2007

MG MGB Technical index

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