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Yesterday my TR6 failed it's MOT


Because when the brake lights (which are LED ) were applied the front side lights also came on. The garage replaced my LED bulbs with standard filament ones the fault went away.


Can anybody explain this or hopefully suggest how I can put the LED bulbs back and prevent the same thing happening.



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Check the earths! Plus the rear filament holders are not the best of designs, and probably just being disturbed to change the lamps was good enough to get a better connection.

The side lights are only 4-5 watts and draw about 0.4 amps, so the LEDs looking for a ground found one through the front side lights.

So, personally I would replace the rear lamp holders and if your good with a soldering iron add an extra earth fly lead and attach to one of the studs that holds the lamp cluster in the car.


Take a look here http://bullfire.net/TR6/TR6-65/TR6-65.html

Ed_Hollin modified his.

Edited by DaveN
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I’ll take a punt!


Its down to dodgy/corroded connections


The brake lights are part of the same bulb as the rear ‘side’ lights


When you brake and power is supplied to one filament of the tail/brake bulb some of the power is finding its way to the side light filament. Hence the rear tail lights get some power, but you cannot see this as the brake lights are brighter, and so do the front side lights as they are connected to the rears.


The power is enough to light an led but not a filament.


Hence the priblem ‘goes away’ with old fashioned bulbs.




Sort out the cause being dodgy connections/earths/corrosion in the rear lights.


Whish is probably easier said than done......



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Its probably due to the type of LED bulbs you has fitted at the rear, if these are 'dual filament'. This seems to be fairly common as some of these bulbs do not have two LED elements, but only one which is fed by high current for the brakes and low current for the sidelights. These are not always properly isolated from each other so when you apply the brakes, current leaks back onto the sidelight circuit. The cure is to fit an in-line diode in the sidelight connection to the lamps which prevents the current flowing backwards. Some LED suppliers can sell you packaged diodes specifically for this fault.


I recently assisted a chap on the Morris Minor forum with exactly the same symptom. The diodes cured it for him.


Although it could possibly be an earthing fault as others have suggested, this is unlikely since the problem went away when you re-installed normal bulbs.

Edited by RobH
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