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MG MGB Technical - 2 terminal vs 3 terminal indicator flasher

I ordered the wrong indicator flasher for my 78 MGB. I currently have the 2 terminal flasher unit and what I received was a 3 terminal one. When I wired the 2 leads up to the 3 terminal flasher, surprise surprise it didnt work. The indicators just stay on instead of flashing. So is there an easy way of getting the 3 terminal one to work? I just dont want to have to return it.
Ross Kelly

Ross. The only difference I know of between the two types is that the three terminal has a separate feed to the panel (dash) indicators and the two terminal doesn't. Make sure you have the indicators themselves connected to the correct terminal.

Mine is marked L P X and I think that L = lights, P = panel repeaters and X = Power but I wouldn't be 100% sure of that. If the panel lights are connected to the terminal that is supposed to power the indicators then it won't flash as the panels don't draw enough current to make the unit flash.


Tony
Tony Oliver

Ross,
You have to take the third terminal to earth. Make up a small lead with a 15amp female spade terminal for the unit and terminate the other end with ring terminal that you then affix to a suitable earthing point.

I used one of these units on my previous MGB and it cured all the problems I was having with slow indicators, they also give the added advantage of an audible 'click' when the lights are flashing.
Mike BGT

Ross, here's how the wires should be connected.

49(+) Input - Green wire.
49a(L) Output - Light green with brown bands.
31(-) Earth - This is the one you have to make up yourself. For correctness all earthing leads on an MGB should be black.

I was able to secure the new unit to the bulkhead using the existing bracket by slighting bending the arms outwards.

HTH

Mike
Mike BGT

Ah lovely. I'll get it installed this evening so! My indicators do flash incredibly slowly and take ages to actually start working (Half the time Ive already gone around the turn I was indicating for!). That and I can barely hear it clicking at all. So it sounds like I did get the right one after all!

By the way, another issue. Its not a major one but is it normal that the hazard lights will only start flashing when the hazard button is on and the indicator stalk is on in either direction? It just seems odd.
Ross Kelly

You have an odd set up there Ross

I changed my indicator relay a few days ago. I had a 3 pin with only two connected. The third one has a rubber insulation boot stuck on it, no earth wire. It still worked.

You must have a wiring fault some where.

Dave
D M Tetlow

Dave,
Ross will have bought a modern electronic flasher unit, I suspect yours is of the original thermal type. The electronic units offer several advantages over the thermal type - they will operate immediately, the flash will always be consistent, they are far less sensitive to voltage variances, give a more audible warning and most of them have a bulb failure indicator in that they will flash twice as quick should one bulb fail.
Mike BGT

Well maybe the case works as the earth as well and seeing as I didnt have the case touching anything it wasnt earthed at all. It wont be tonight when I get this sorted out. Im taking an x-trail home from work to show a customer so my car is staying safely locked up in the job. WHen I try it Ill let you know what happens. Whats the verdict on the hazard light thing though? Any ideas there?
Ross Kelly

My 73 doesn't require the turn signals to be on in one direction or the other for the hazards to work. (Although I'll admit my hazard switch, despite my best attempts at cleaning it, has its own mind as far as when it wants to work and when it doesn't). Suggests that something is amiss in your wiring. A great resource in case you haven't had this suggested yet, is advanceautowire.com (I have no financial affiliation) they have wiring diagrams for all years of MGs as well as other vehicles. These diagrams are much easier to follow than the ones in your MG owners manual. You can save to disk, bring the disc to a print shop and have it enlarged and printed in colour which makes any electrical sorting much easier. You can laminate it and use non-permanent marker on it if you need to.
Erick Vesterback

Mike.

Your stop on. I did buy the old tin can type. It has a earth holder attached to the body. The thing is a bit Heath Robinson but did work, even hanging free on its two wires. This new one only had 2 pins.

The reason I played around at all was due to the Hazard switch playing up. The indicators work through the hazard switch, so it can be a real pain. My actual problem was when turning the hazards on, which can be done with the indicator switch in any position, the indicators all flashed but only one of the tell tales flashed!! Wiggling the hazard switch solved this.

I ended up with a round 2 pin flasher for the hazards to get me through the MOT. The MGOC has since supplied me with a new switch and the correct oblong hazard flasher.

Dave
D M Tetlow

I couldnt get the thing to work. Regardless of whatI tried, the indicators didnt flash. They just stayed on. I think I must have gotten a duff flasher. Seeing as for the sake of €7 Im not going to bother returning it I will try cracking it open to see if its something simple wrong. Its brand new though. It was in a vacuum pack.
Ross Kelly

Its the bloody same inside as the onel I already have but is clearly faulty. It was made wrong. Where can I pick up one of these electronic indicator flashers? Will one from another car do?
Ross Kelly

Ross,
You can buy generic electronic flasher unit from most car spares shops or motor factors. Cost about £5. Look for one with bulb failure warning, it's well worth it for safety.
Mike BGT

Yeah my local car parts supplier does them. I'll pick one up during my lunchbreak and hopefully I'll be in business then. I'll report back later.
Ross Kelly

I got me a 2 terminal one today in the local motor factors. Its smaller than the one I have now and says 21w x 2 + 5w on the side, which I reckon should be just the job. We'll see soon enough how it works out.
Ross Kelly

Well I fitted the new flasher today. Its not working perfectly. Sometimes it wont flash, and will just buzz and the lights flicker. I reckon its not getting enough power. I replaced the spade connectors and the fuse holders contacts which were a bit corroded and I sprayed the indicator switch full of WD40 in an effort to try and clean it out. Any other suggestions? When it does work it clicks loudly and more evenly. It make a nice sort of dih-ding sound as well, as opposed to the normal clicking youd expect.
Ross Kelly

Ross, have you measured the voltage on the green wire to see if you are getting at least 12 volts? I would tend to agree with you that there may not be quite enough voltage to power the flasher causing it to act erratically, also given that you've tried a few flashers now and none give the correct results. When the external signal lights are lit, do they seem bright or alittle dim?
Referring to the wiring diagram (Late model UK MGB) provided by advancautowire.com, the power in the green wire to the flasher comes through the hazard switch, which can be temperamental. There may be some dirt or corrosion inside that switch which may be causing resistance in the circuit, reducing the voltage at the flasher. There are also two fuses - one with a white on one side and a green on the other located under the hood I believe (I may be wrong), and another with greens on both sides, located under the dash. These could be an area where corrosion is increasing resistance.
Bad grounds at the light bulbs themselves can cause dimness or different rate of flashing, although it would be odd for all the grounds to be equally bad on both sides.
Hope that helps,

Erick
Erick Vesterback

My hazard switch is knackered in fact. One of the jobs Ive to do is to replace all my dashboard switches. All of them except the one for the fan are broken. I'll see if I can patch it up to get it working in the meantime though. I'll check that out about the fuseholders too.
Ross Kelly

There are two types of 3-terminal flasher unit - one used on MGBs from the beginning to 67, the other is an electronic unit used on modern cars. The two are conencted differently. The third terminal on the MGB item is used to flash the dash tell-tale lamps via additional contacts in the indicator switch, on the modern item the third terminal is connected to ground or earth.

The difference between the two (and between the MGB 2-terminal flasher used in the remainder of production) is that the MGB items stop flashing when one indicator bulb has failed and the other bulb glows permanently, whereas in the modern electronic version the remaining working bulb flashes at double speed. Unfortunately many modern drivers are too stupid to recognise this distinction and drive around oblivious to the fact that one of the corners isn't working, even though both sides flash at different rates! The benefit of the modern items is that they aren't so susceptible to bad connections and low voltage which give slow flashing rates as the original items.

There are also after-market so-called 'heavy-duty' flasher units that don't have a bulb failure warning mode and are a hazard - pun not intended.

There are also two significant differences between indicator and hazard flasher units in that indicator units lights the lamps *immediately* the indicator switch is operated, then after a short pause start to flash off-on-off-on. Hazard flasher units do nothing when first switched on for a short periods, then start flashing on-off-on-off. Again the difference is a safety issue. The second difference is that hazard units are designed to flash at more or less the same rate regardless of how many lamps are lit and on reducing battery voltage i.e. after a breakdown or accident, whereas indicator units will give a different flash rate (i.e. stop flashing to flash at double rate) if one bulb has failed.

But if you have indicators that work correctly sometimes and not others, then you have one or more bad connections somewhere. Your hazards should work independantly of the indicator stalk, if they only work when it is operate one way or the other they are incorrectly wired as well.
Paul Hunt

Well the one I have now is a 2 terminal one but I reckon its a relay with a timer circuit as opposed to a bimetallic strip and heater (daft!). Anyway it buzzes sometimes when the switch is turned on but will eventually start flashing, albeit erratically and will sometimes buzz as well then. It has to be a loose connection somewhere. Ill have a look over the weekend. Its probably something simple.
Ross Kelly

If both sides react the same either the problem is from the indicator switch back towards the fusebox, or the flasher unit. If the latter, then the original type unit is not so daft!
Paul Hunt

It does the same both sides. One side flashes faster than the other too but I dont mind that so much. The fact that it took a while for the indicators to start working and theyd flash very slowly with the old one would say to me its the connections. My multimeters battery is dead so I cant check the voltage until I get a new battery. The fuseholders terminals are cleaned up now. I need to work back and try to find the source of the problem.
Ross Kelly

Take a flying lead from a known good battery connection direct to the B terminal (green wire) on the flasher unit and try then. If that is the same then it is the flasher unit. I don't know what type of flasher unit you have but if it buzzes that sounds more like problems with the unit than connections. Any lettering on the can? Electronic types usually need 3 terminals.
Paul Hunt

This thread was discussed between 19/05/2008 and 26/05/2008

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