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MG MGB Technical - Another turn signal problem

Going thru the wiring on my 77B. P.O. had every thing all jumbled up. After many hours of reading ( thanks to Paul Hunt's and Rick Astley's site ), I think I have it correct or very close to it. After replacing the Hazzard switch(gone) adding new flashers, bulbs,and wiring the system correctly (I think), I got everything working. The flashers work properly but the turn signals start to work normally for a couple of flashes then flash at an extremly fast rate. The bulbs are working front and back but flashing at a frantic speed. Is there a way to correct this problem?
Dan H.
Dan Hanson

Hi Dan

A clue.. A bimetallic strip flasher tends to get faster as the load current increases.


Does the problem happen on both sides of the car ?.

Don
Don

Hi again.

I have had a ponder, and suspect that there is a problem around the hazard switch or it's associated wiring.

Did you buy a new one ?.

If I remember rightly, operating the hazard switch :

1) connects the two sets of lights together and

2)switches the feed from the indicator switch and indicator flasher to a different feed from the battery via another flasher module.

I suggest that you remove one of the wires from the hazard flasher unit (the flasher module). I suspect that your indicators will then work normally. (But the hazards won't).

It is possible that you still have to cope with the fault that originally made the PO rewire things.

Please let me know the result if you try this, and we can try to make further progress.

One final thought.. has the car suffered the all-too-common wiring meltdown following a short in the wiring to the overdrive switch ?.

HTH.. Don
Don

Hello Don,
The ultra fast blinkers problem is on both sides of the car. Start slow (normal) then speed up as if a bulb is out but all bulbs are working. The hazzard switch is new. Purchased new flashers from a local auto store. The overdrive switch, (If that is the component located on the brake/ clutch housing cover), is now disconnected. I installed Webber carb, header, dizzy, and all smog stuff removed. The wiring to the overdrive switch ( if I described it right)was fried. I will try your suggestion of removing one if the wires from the flasher module.
Dan H.
D.E. Hanson

Hi Dan

It seems that your car has suffered from a common problem with models having the overdrive switch in the gearknob. The overdrive activation wires insulation chafes and allows a short to chassis, which fries the wiring.

I suspect that if you remove the insulating wrap from the loom in the vicinity of the fuse box you will find more 'fried' wiring with insulation damage.

Melted insulation allowing shorts between wires could be your (and the PO's) problem.

Don
Don

Don, not sure of the overdrive switch in the gearknob.
The item I'm talking about appears to be a vacuum switch located in the engine compartment on top of the brake/clutch cover.
Would I have an overdrive switch in the gearknob in a non-overdrive car?
Dan H.
Dan Hanson

OE turn signal flashers will go fast if they they are supplying too much load i.e. three bulbs (ignore the tell-tale on the dash unless it is more than 2.2w) or two bulbs of a higher wattage than should be. The usual problem is slow flashing because of insufficient current due to bad connections. Modern replacements will flash at double-speed if one of the bulbs is out, but if both bulbs were working but were of lower wattage than should be you would get a similar effect. Hazard flashers are designed to operate one to four bulbs with very little change in speed (which is why they should never be used for turn flashers). All the hazard switch does for the turn signals is to connect the 12v supply to the turn flasher when the hazards are off. If the contacts that joined the two sides together were stuck closed you would get fast flashing with the OE flasher and all four corners flashing, but then, that would be obvious from looking at the lights.

It is not an overdrive switch on the 77 and later firewall but the Transmission Controlled Spark Advance solenoid that controls the distributor vacuum advance, which operates in 4th gear only controlled by the same gearbox switch that is used to override the OD, if you have OD. If the wiring to this solenoid was fried it implies a short-circuit in the solenoid itself.
Paul Hunt

Paul,Don Thank you. What I did was use a Hazzard flasher for the turn signals, didn't know there was a difference. And it was the TCSA switch that had the fried wiring. I currenly have the TCSA removed due to swapping out the dizzy for a euro spec dizzy w/ vacuum advance and Webber carb. I guess this is OK???
Paul great web site. So much info. I am learning a lot and hopefully continue to do so. Thank you.
Dan H.
Dan Hanson

Hi all.

Thanks for the info, Paul.. I wasn't aware of the new flasher type.
I guess it would be useful if we knew which type we are dealing with.

I am not familiar with US spec cars, but I guess that any fried wire that enters the loom may cause damage to the loom, which may not be obvious until the loom tape is removed. In my own case, the usual gearlever overdrive switch problem caused significant hidden damage to the loom.

Please keep us updated, Dan.

Don
Don

Don you are absolutely correct. I have found the "hiddden damage" in a few places. Especially the white wires near the inertia switch. Thanks again for the info. I would suggest to anyone who has electrical problems to remove some loom tape in areas that are suspect and repair any damage short of replacing the entire harness. You can purchase the correct blue loom tape. Thanks again.
Dan H.
Dan Hanson

"any fried wire that enters the loom may cause damage to the loom"

Indeed so. The TCSA and overdrive are fed from the white which is unfused ignition. After several reports here and elsewhere of loom fires after wiring shorted out - particularly the later gear-lever mounted manual switch due to its continual waggling about - I fitted an in-line fuse to both my cars. On the roadster with the switch on the dash I fitted it at the switch, on the V8 with the column switch fitted it where the yellow in the main loom joins the yellow/red in the gearbox loom. The fuel pump is the same, and both my cars have suffered loom damage (before my ownership) because of a short at or close to the pump. Again an in-line fuse fitted where the main loom joins the rear loom limits the risk. Replacing the rear loom is *not* something I would wish to tackle again, by contrast replacing the main loom is far easier, but avoiding replacing either is best of all.
Paul Hunt

This thread was discussed between 15/10/2003 and 17/10/2003

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