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MG TD TF 1500 - Tail light middle brake light mystery

I have a question for you guys that know a lot more than me about the wiring. I have restored my 1954 MG TF and in fact am driving it to be in the Greenwich CT COncours - maybe a first for a TF, not sure. Anyway, I have one of those nice Moss 3rd lights/brake lights mounted on my luggage rack. I tapped into the right brake light white/purple and the third brake light works. It also blinks when I turn the left signal on. I though that was pretty neat and wanted to have it blink when the left signal was on, to increase visibility. So I tapped into the hot middle light wire (which was tapped into right turn light) on the white/brown wire. Two things happened - The left worked as it should and blinked the middle light.

Now the dash green indicator had always blinked when I turned right, but for left it only blinks once and then stops even though the outside turn signal are blinking as they should. When I hooked up the third brake light, it blinks as normal on the dash. Why would this be??

Here is the strange thing and I don't expect anyone to answer - the next day when I tried it out, when I turned either signal on, all three lights blinked. Don't know why and no logical explanation.

Here is my second question for you - do you know how I could wire it so the middle brake light blinks when I turn the signal on left or right, but doesn't make both turn signals blink? Thanks, Keith
K E MURPHY

You would have to wire the light from both brake lights and run the wire through a diode...so it can be done...but I would imagine it is probably illegal and I believe I would find it pretty confusing as to what your intentions were if I was following you.
MG LaVerne

Keith - Your third brake light needs to be wired directly to the brake light switch instead of either of the brake light/turn signal at the rear lights. Cheers - Dave
D.W. DuBois

Keith, If you drive fast enough then what is behind you is of no concern.Tom
tom scott

Keith, Dave is right.

A longer answer: the tail lights are powered through an 18th century system of ropes, hinges and coal fired furnaces. As the power that is supposed to go to the brake lights passes through Brittanham-on-Briggsandstratford it stops for a short chat with Mr. Lucas's heirs. There, a set of instructions is passed along to the now totally overwhelmed electrons. After fighting their way along an impossibly convoluted nest of cracked insulation, rusted terminals and barely capable wires, 7 or 8 relays are encountered. Only if the one, single, barely working relay is chosen do the damned lights go on.

Keep a camera handy. If the lights work you'll want to have someone take a photograph of the event. You may never see this again.

....
MAndrus

Mitch - Have you ever considered writing dialogue for science fiction movies - I have struggled through much less believable (not to mention humorous) dialogs than your above missive. Cheers - Dave

There you have it Keith, the real way to get your third brake light working properly ;-)
D.W. DuBois

Thanks for all the good and amusing perspectives gentlemen! I will think if I want to have the middle work as only brake light or to also blink when turning and have only one side blink.

Question - in past when I turn right, my green light on dash blinks, and when right just blinks weakly once. Then when I wired the middle brake light up to both sides, the green dash light blinks normally. Wonder why?
K E MURPHY

Either a bad ground or a flasher headed south Keith. If you decide to go with the brake light only, you can take the source near the rear of the car off one of the bullet connectors. You may need a dual connector instead of a single. I did that with my Christmas Santa. I had it wired up with a dual filament bulb. Had it as a park lamp but it would go brighter when I stepped on the brake.

MG LaVerne

"If you decide to go with the brake light only, you can take the source near the rear of the car off one of the bullet connectors."

That is not correct. If you take the power for the third brake light off of either of the sockets for the standard brake light, you will also get the third brake light blinking with the particular turn signal is activated. The third brake light has to be connected to the brake light switch, before it goes into the turn signal relay. Cheers - Dave
D.W. DuBois

Brain Fart Dave...You can do it if you strung another line from the switch to the back of the car...and then forgot you did it that way for future use. Duh?

Yes Keith...run it from the switch.
MG LaVerne

This thread was discussed between 29/05/2015 and 30/05/2015

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