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MG MGB Technical - Another turn signal problem

After replacing the engine in my 79 MGB I discovered the turn signals no longer work. The emergency flasher work in fact all the other lights work OK.

Can anyone give me some ideas where to start troubleshooting.

Also where is the flasher unit located? I see 2 units on the right side of the engine compartment that kind of look like a flasher unit but I do not think hey are. While testing theses units one of them turned over the engine the other turned on the fan.

Any ides would be appreciated.
Bob

I am pretty sure that both turn signal indicators are wired together with the emergency flashers. I used to have this problem when it was damp out all I did was turn the emergency flashers on and off and it usually just flushed itself out eventually. Not very systomatic but it seemed to straighten it right out.
Josh

The flasher for the turn signals is located behing the glove box on the firewall. The flasher for the hazard warning lights is located behind the radio console. They are not interchangeable.

The turn signals work through the hazard warning swith. If corrosion builds up on the contacts, your flashers will work but not the turn signals. Sometimes several pushes on the hazard switch will get the turn signals to work for a while, but the real fix is to take out the swith and clean the contacts.

Jim
74B Roadster
James Conner

Those two boxes in the engine compartment are the starter and ignition relays. The flasher units are in the cabin under the dash on the firewall, one immediately above the other on the RH side on an 1980 RHD car. The turn flasher has green and light-green/brown wires going to it, the hazard flasher has brown and light-green/brown wires going to it.

The turn signals are wired through the hazard flasher switch in the off position. If none even light then this switch could be the problem, or it could be the turn flasher itself. With the ignition on check with a voltmeter or test-lamp on both sides of the turn flasher unit, with the turn signals off and on. If there is no 12v at all it is probably the hazard switch. If there is 12v but only when the turn signals are off ditto. If there is 12v on the green but not the green/brown the turn flasher is bad. If there is 12v on both all the time there is a break in the light-green/brown up to the turn flasher switch, por the switch itself is bad.

The hazard flasher switch can be dismantled, cleaned and reassembled, but do it in a clear poly bag to catch all the bits.
Paul Hunt

After reading Paul's step by step fault diagnosis I think I know the answer to my turn signal problem...break in the light green/brown wire.
I have 12v on both poles of the new (and old) flasher at all times (ignition key on or off, turn signal switch on or off).
The hazard switch works as it should, and all four lights plus dashboard lights blink.
I've checked all four fuses in the fuse box, and all three in-line fuses near the fuse box. All OK.
I also tried plugging in a new turn signal switch that came with the car, but that changed nothing.
So, where should I begin? I think Paul said to start at the battery and check voltage up to the flasher. I'm not sure how to go about that. Rather than start pulling apart the wiring harness, I thought it would be best to start with the list, and gather any ideas that could help me find the problem.
Thanks,
Randy
1977 MGB Tahiti Blue with twin SU's
Ithaca, NY
Randy Olson

"I have 12v on both poles of the new (and old) flasher at all times (ignition key on or off, turn signal switch on or off)."

On the turn flasher there should only be 12v on both terminals of the flasher unit with the ignition on, not with the ignition off. However the HAZARD flasher should have 12v on one of the terminals all the time, ignition on or off.

You say the hazards work as they should, what happens when you operate the turn flasher switch with the engine running - do the lights that side and the tell tale light but not flash? On not even light? Are both sides the same?

If they light but don't flash then either the turn flasher unit is faulty, or insufficient current is flowing to trigger the flashing. In the latter case it could be because of bad connections anywhere in the circuit, or one or more incorrect wattage bulbs.

If they don't even light, but you have 12v on both terminals of the turn flasher unit, and the tell-tales flash with the hazards, then there is a break between the turn flasher unit and the where the turn flasher switch joins the rest of the harness, i.e. connections as well as the switch itself.

If both sides are the same then this could well be the light-green/brown, between the flasher and the switch, or both the green/white and the green/red between the switch and the main harness.

You will have to check for 12v on those three wires at the switch contacts, and where the switch tail plugs into the main harness.
paulh4

Thanks for the response. I just checked a few things and here's what I found:
The flasher module has 12v on both terminals when the ignition is off.
The flasher module has 12v on both terminals when the ignition is on.
The hazard module has no power at either terminal when the ignition is off or on.
When I tried the hazard switch this time, the module clicked, but the lights didn't flash...not the four at the bumpers, or the tell tales on the dash. The word "hazard" illuminated on the dash. So, I wiggled the hazard switch connection under the dashboard where the switch is located and voila! the lights all worked. The connection at the switch was loose.
I rechecked to see if reconnecting the hazard switch changed whether there was power at the hazard module, but there still was no power on either terminal.
Yesterday, with the engine running I tried the turn signals, and they didn't work. No lights at the bumpers, and no tell tales.
Where the turn signal cluster of wires connects to the main harness I disconnected the switch and found there was no power on the light green/brown, the green/white, or the green/red wires. That was checked with the ignition off.
Let me know if this information helps you point me in the right direction.
Thanks again,
Randy
Randy Olson

One of the complications is that the wire from the turn flasher to the turn switch, and the wire from the hazard flasher to the hazard switch, are both light-green/brown, but they are separate wires. It shouldn't be possible to get them mixed up as they should each be wrapped with their other wire i.e. brown for the hazard flasher unit, and green for the turn signal flasher unit.

I can only reiterate that for the turn flasher, there should be not be 12v on either terminal with the ignition off. The other wire on that flasher is the power supply which should be green, which is fused ignition, hence no power with the ignition off. This wire comes from the hazard switch, and there should be another green on the hazard switch. Those two greens should be connected together with the hazards off, and disconnected from each other with the hazards on. Dicky hazard switch contacts can stop the turn signals working, as well as affect the hazard lights.

Also for the hazard flasher there should be 12v on the brown wire at the flasher unit all the time. However there is an in-line fuse in this wire - with brown both sides, which if blown would obviously stop the hazards working, but won't affect the turn signals.

So you have two problems at least:

1. Power apparently being on the green and light-green wires at the turn signal flasher unit with the ignition off - the reason for this can't even be guessed at - unless the hazard switch has been connected incorrectly or is faulty.

2. Even though you have power on the light-green/brown at the turn flasher unit, you don't have it on the light-green/brown harness wire at the turn switch. This can only be - assuming you have the correct light-green/brown wire in both places, that the wire is broken somewhere.
paulh4

Attached is a photo showing the hazard module and the flashing module, and the associated wiring to each. Based on Paul's information, I don't believe they are wired properly.
I know the previous owner changed the flasher because the old one was in a box of spare parts I got with the car. It's possible that the wiring was mixed up when the flasher was changed.
I would like to know which wires go to which modules. And, equally important, what wires go to which poles on their respective modules.
Thanks again,
Randy


Randy Olson

That looks OK to me, the hazard flasher is often quite large and cylindrical (although the two would originally have been very similar as indicated by the two clips), the turn flasher rectangular.

Hazard flasher uses brown and light-green brown wires, turn flasher uses green and light-green/brown.

The two pairs of wires seem to have blue tape around each pair. Of course that may not be original so if all four come out of the same place in the harness then they could be mis-matched, however the main harness wrapping is also blue.

It doesn't actually matter which wire goes on which terminal as they are both 2-wire devices and not earthed, however the convention is to have brown and green on the B(attery) terminal, and the light-green/browns on the L(amps) terminal - if they have those designations moulded into the bases.

If just the supply (brown and green) wires had been swapped between flasher units, the effect would be that the turn flasher would be available all the time i.e. ignition off, wuth the turn flasher unit clicking, but the hazard flashers wouldn't work at all.

If just the load (light-green/brown) wires had been swapped between units it's a bit more complicated. Again the turn flashers would be available all the time, but it would be the hazard flasher unit clicking.

The hazards would only operate with the ignition on, but as it would be the turn flasher powering all four bulbs it would almost certainly burn out, after flashing very rapidly when first tried.

I think the above is correct, I haven't tried it.

It depends whether they have always been like this in your ownership, or just started doing it after you did some work on the car. If the former, then there could be any number of wiring and component faults. If the latter then it should be more straightforward. You need to write down clearly each test you do, before you do it, and what the result was, immediately after you did it. After two or three tests it's very easy to get mixed up as to what the tests and results were when you write them here.
paulh4

I tried a couple of things, with interesting results.
First, without changing the wiring from that shown in the photo, I tried the Hazard switch. The tell tales worked, and the passenger side lights at front and rear worked, but not the driver's side.
Then, I put the Green wire on the cylindrical flasher, and the Brown wire on the rectangular flasher. The Hazard lights did not work at all. But, the turn signals worked on the passenger side only, with either the ignition on or off.
Could it be that the the other flasher is bad, too?
I also rechecked the in-line fuses under the bonnet, and cleaned the connections on the Green wires at the fusebox. Nothing seemed to change.
Could a faulty Hazard switch be causing these problems?
Thanks for your continued support (and patience!),
Randy
1977 MGB
Randy Olson

I try not to use my hazard flasher if I can help it. It seems that every time I do, something goes haywire with my turn signals. RAY
rjm RAY

"I tried the Hazard switch."

Did both tell-tales on the dash flash? Or only the passenger side like the external lights?

If the latter then the hazard switch can cause that. It's generally so rarely used that the grease hardens and acts as an insulator. Sometimes flipping the switch on and off a few times helps, but in the end I had to open up the switch, dig out the old grease and replace, and after that they have been fine.

If the former, then on a US 77, it could be bad connections where the rear and main harnesses join in the engine compartment at the firewall, in the green/white wires.

Rather than trying multiple things by swapping wiring round, or trying to fix all the faults at once, it will be easiest to pick one fault and follow that through to a conclusion.

So with the brown and it's paired light-green brown on the round flasher unit, the ignition off, and the hazard switch on, track the voltage through the circuit - brown and light-green brown at the flasher unit; light-green/brown, green/white (passenger side), green/red (driver side) and light-green/purple (console tell-tale) - out to the corners of the car. When you get all those flashing then you can look at the turn signals.

Incidentally, do either of the flasher units have any numbers on them? Often they indicate the maximum wattage and current they can handle, for example turn flashers having something like "2 x 21W + 5W" and/or "12A max" and the hazards "4 x 21W".
paulh4

In answer to Paul's questions, both left and right tell-tales on the dash blink when the Hazard switch is activated, but only the passenger side exterior lights blink.
As for the flasher unit numbers, the original rectangular Lucas is marked 9FL Flasher 12V 12A Max,
35053 A 38 76. The newly purchased cylindrical NAPA flasher is labeled EL 12, 2P 12V, 09216 Flasher; on the opposite side it says Max 25 amp.
Randy
Randy Olson

Those flasher units are correct - or at the very least what I would expect to see.

With both dash tell-tales flashing but not the drivers side exterior lights, I suspect the 4-way bullet connector in the mass near the engine compartment firewall, where two green/reds from the main harness join the green/red from the rear harness.

Either that, or you have a fault in the front circuit and another fault in the rear. Check both sides of the 2-way bullet connectors, one by the drivers headlight and one in the boot/trunk near the drivers rear cluster.
paulh4

Right again, Paul. I cleaned the bullet connectors on the red/green wires and the Hazard lights all work as they should. Those were very hard to get apart to clean, and I feared I was going to break the wires trying to pull the bullets out of the connector.
I tried the turn signals and they still don't work. These I need to get fixed. I thought replacing the flasher unit would solve the problem. But, I believe the new flasher unit is on the Hazard circuit since its connected to the Brown wire (see previous photo).
I'm thinking maybe I should check other bullet connectors that are on the turn signal circuit. Let me know if anyone has a better approach.
Thanks once more,
Randy
Randy Olson

Since there was not 12v at either pole of the turn signal flasher with the ignition on, turn signal on or off, I suspected the Hazard switch might be bad. I managed to remove it from the dashboard, and clean all the terminals on the switch and the connector. Then, I tried to find 12v at the turn signal flasher. Nothing.
So, I took the switch apart. The inside didn't look too bad, so I carefully put it back together. Tried to find 12v at the turn signal flasher, but still no luck.
Maybe I need a need Hazard switch, but before plunking down $20 plus shipping I want to know if there's anything else I should be looking at.
Thanks,
Randy
1977 MGB
Randy Olson

Reading through the archives I came across some of Paul's notes, and have a few more clues to the turn signal problem.
Paul's note: "Check the connection between the main harness and the indicator switch sub-harness, and the switch itself. In the former case check the two halves of the connector are fully pushed together, and none of the pins has been pushed out the back which can happen." MINE SEEM OK.
"With the hazards on you should see 12v coming from the green/red and green/white wires in the main harness into the indicator harness." I HAVE 6v WHEN THE FLASHERS BLINK.
"With the ignition on and the hazards off there should be 12v coming from the light-green/brown in the main harness to the indicator harness." I HAVE 9v.
"With the indicator switch operated one side or the other there should be 12v coming from the green/red or green/white of the indicator harness into the main harness." I HAVE ZERO VOLTS. THAT'S WITH THE IGNITION ON.
I'm not sure what this means, but likely someone does know. If you can point me towards possible culprits I will check them out.
Thanks,
Randy
1977 MGB
Randy Olson

Your image shows the brown wire on the round flasher unit, which is the hazard flasher going by the numbers you gave.

The 12v i.e. fused ignition supply on the green wire to the turn flasher does come through the hazard switch, in the off position, and this is a common source of problems for the reasons I gave above. There should be two plain green wires on the hazard switch - one is from the fusebox, the other is to the turn flasher unit. If you have 12v on one (with the ignition on) but not the other then the hazard flasher switch is faulty. If there is not 12v on either green wire, then the fault lies back towards the fusebox. On the US 77 there is a six-way bullet connector, and a 4-way in that circuit, so I wire could have pulled out of one of those. The 4-way is closer to the turn flasher and feeds other circuits as well so if some at least of those are working power is at least getting as far as that 4-way. The other circuits are the time-delay buzzer linked up to the seat-belt (but that may not be working anyway), the column wiper switch, the tachometer, and the instrument voltage regulator for the fuel and temp gauges. So assuming some of those are working, either the wire feeding the hazard switch has pulled out, or has failed in some other way.

Ignore your voltage readings for the time being as they will probably only confuse. First get 12v at the green wire on the turn flasher unit, then we can diagnose further from there.

paulh4

The two green wires at the hazard switch have no voltage. So, I found the four-way connector in the engine compartment and cleaned all the connections. Checked the turn signals, still not working. And, there was still no voltage at the green wires at the hazard switch with the ignition on.
I did not find a six-wire connector, unless you are talking about the connector that plugs into the hazard switch. It has 6 holes for the six prongs on the hazard switch. These have all been cleaned. I also checked the wires at this connector; they all seemed OK.
So, did I find the correct six-way connector? Or, is there another somewhere between the hazard switch and the fuse box?
Thanks for all your help,
Randy
1977 MGB
Randy Olson

Sorry, the 4-way and the 6-way (for bullets, not the hazard switch) will be behind the dash somewhere.

If all those other components work OK then it has to be a break in the wire between the 4-way and the hazard switch. If you can't find that then you could just find a green connection somewhere convenient that DOES have 12v with the ignition on, and connect that to the hazard switch. You will have to determine which of the two greens there are which, the simplest way is to do a continuity check from each of them in turn to the green at the turn flasher. The one that doesn't have continuity, is the one you will have to replace.
paulh4

Yahoo!!! The electrics now all seem to work as they should.
As with most electrical problems that I need to deal with, the reason that the turn signals and everything else is still somewhat of a mystery. My best guess is that the four-way bullet connection with the green wires was corroded. Cleaning it yesterday didn't seem to solve the problem with the turn flashers. But, today I decided to just drive the car and see what happened. It was a nice drive!
The car started even though the battery had been drained from all the testing and no driving. Out of habit (by now) I tried the turn signals. Nothing. Hazard lights worked OK. Then I tried the horn...nothing. Headlights...nothing. At this point I thought things were really going in the wrong direction. But, out of the garage we went.
Driving along I tried the turn signals and horn. Still not working. All the dashboard gauges seemed to be working fine. As I was driving I went back over a mental checklist of what I had recently done that might have screwed up the wiring to the headlights and horn. All of a sudden I looked down at the wiring dangling above my left knee and saw that I had not reconnected the turn signal/horn switch to the main harness. I pulled over, and snapped the connector together. I tried the horn...it worked. I tried the turn signals...they worked better than ever! Headlights worked, too.
So, now I can go back to watching a little more Wimbledon, and open a bottle of Old Speckled Hen. And later in the week, do a little British-car motoring.
Thanks a lot for all the help,
Randy
1977 MGB, Tahiti Blue/tan
1969 Jaguar E-Type 2+2 BRG/tan
Randy Olson

Perseverance and logic got there in the end. There's no better faulting technique than "What did I do last? ..."
paulh4

This thread was discussed between 25/03/2002 and 28/06/2016

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