As the brake light circuit is teed into the tail light wiring, the current travels down to the rear light at full current, as it bypasses the resistor when the brake is used. But the current also travels back towards the light switch and is connected to the switch on the output side and not on the power-in connection. The mechanics of the switch will determine if a diode is needed. When a switch is off the brass roller will sit between 2 terminals that do not connect to the power-in connector. But with the brake circuit sending current back to the output connection, who knows what it's connecting to. This will also change as the switch is moved to each position and the roller moves, so you could find you have a short circuit, or send power somewhere you don't want it, when the brake is used. You could test the switch in each position and try the brake, or simply put a diode in the circuit. It will depend on what switch is being used and as Rik has pointed out, seems to work ok on a WD switch. I look at it as, sending a power feed to the output of a switch is not a good idea and could cause problems.

email (option): horror@blueyonder.co.uk

When i fitted mine Ian, unknown to me the headlight came on as well when i braked, now have an ordinary one fitted untill i get my arse into gear and fit a diode i think thats what its called (electric only goes one way when fitted apparently?)

It will depend upon weather you are using a single element or a duel element globe & wiring.
A dual element LED globe has a diode in there to prevent back flow via the tail lamp connection when you brake without the lights turned on.

If you are using a single filiment globe and holder then you will need to put a diode in the tail lamp wire from the light switch to the tail lamp.

A lot of cheap LED replacement globes just use a resistor to dull the tail lamp and bypass the resistor for stop lamp.
A good quality light board OTOH will have seperate LEDs for the stop and tail light functions.
The bulbsthatlast4ever tail lamp I bought back in the 90's that has worked flawlessly is wired this way.
Then again it was over $ 100 back then, but money well spent.
Now LED's are mainstream & not exotic the prices have crashed and so has the quality .

email (option): bsansw1@tpg.com.au

Yes, I was talking about a brake light conversion for an original back light with a single filament bulb. With a dual filament bulb you have 2 separate circuits so there isn't a problem.

email (option): horror@blueyonder.co.uk

Hi all just fitted one off those led headlight bulbs that's been spoke about , my problem now is that with the light switch off the head light is still on , switch to tail light only and it goes out any ideas anyone cheers Phil

Yes! Your wiring is wrong. The bulb can only light up if there is power going to it. Ron

email (option): ronpier@talk21.com

At Founders Day last weekend I bought an LED array that fits into my single filament rear light...

It doesn't use the bulb holder but mounts in front of it (mounting posts included) when the bulb is removed...However, I think the bulb contact plate will need to be removed to allow the wires to exit the rear of the light..

The array has red and white LEDs so it has number plate illumination as well as a rear light and brake light function...

I haven't actually read the wiring instructions as yet as I have to make the rear number plate and light mounting before fitting it up...

I got it from Paul Goff who has various versions, 6 or 12 volt but all for rear lights..Ian

email (option): ian@wright52.plus.com

If the fault has only just appeared and you haven't touched the switch wiring, then it is presumably due to the fact that the LED lamp is illuminating with a current that wasn't sufficient to power up a conventional bulb.

Could it be feeding via a stop / tail if there is a bad earth ?

A couple of photos of the main switch type (and the rear showing the wiring) would be helpful.

I couldn't be arsed with that Goff LED light board stuff. I just bought a direct replacement plug in stop/tail bulb with number plate illumination.

'Part 3' on this page.

http://www.dynamoregulatorconversions.com/stoptail-lamp-bulbs-shop.php

Ron

email (option): ronpier@talk21.com

I have a Miller rear lamp with a small 'screw in' single filament bulb..

Taking that and the overall dimensions of the light itself into account, which is fairly shallow from front to rear, I thought the light board was the best solution in my case..Ian

email (option): ian@wright52.plus.com

OK Ian I know nothing about that Miller lamp. All my Miller lamps accept the normal stop/tail bulb.......You're not riding a Corgi are you Ron

email (option): ronpier@talk21.com