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MG TD TF 1500 - Adding 3rd brake light

I found a sweet 3rd brake light with 2 10W incandescent bulbs, mounted left and right.

Can anyone see a problem in wiring these to the originals so they flash too?

Series or parallel?

.....
MAndrus

Picture?
Mort 50 TD

Generally they should be in parallel with the normal flasher bulbs. If you put them in series they and the normal bulbs will be dim, less than about about 1/4 as bright as in parallel.

Jim B.
JA Benjamin

Mike, you would assuredly want to install a relay in the brake lamp circuit, See http://www.ttalk.info/Tech/BrakeLightRelay.htm (Parallel) Bud
Bud Krueger

Mort, pics soon.

Jim, yes parellel. Just wondering about the load (draw) of an extra bulb on the circuit.

Bud, If wiring these to flash doesn't work out, brake alone will do fine. Thanks for the relay schematic. I have one left over from the 34 Ford build last year.

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MAndrus

Use LEDs and you won't have to worry about the additional draw...
Geoffrey M Baker

Mike - Does you TD have turn signals on your car, and do you want the high mounted brake lights to flash with the standard lights, you will run into problem with the flasher unit not wanting to handle the extra current. You will need to get a different flasher unit and I don't know which one to tell you to get. If you just want them to be brake lights, you can do that by wiring them up to the terminal of the brake light switch that has the green/purple wire on it.

Bud is correct in saying that you will probably need to put a relay in the circuit to handle the extra current. Bud has my directions on how to make up a relay circuit to put in the line, or I can make on up for you. Cheers - Dave
DW DuBois

Mate

It is not the turn signal relay can that is supplying current to drive the blinker lights, it is the blinker/brake relay box. The size of these relay contacts would handle 10Amps.

During the process of installing rear turn signals on my TF I made a blue and had both the original red lights plus my new incandescent bulb amber lights all blinking. No damage to the relay box and only took some thought to resolve my mistake.

Totally agree it is a necessity to install a relay driven by the brake pressure switch prior to adding additional lights in that circuit.

Dont know the legislation regarding having non original red lights as blinkers in your part of the world, I would be checking with authorities.
G Evans

Having switched my existing rear running lights/brake lights/turn signals to LED, I am using only a fraction of the power previously needed on the rear circuit. I could add a large array for a 3rd brake light and still be using less power. No relay needed. Plus I am putting out considerably more light than before...
Just saying...
Geoffrey M Baker

Having switched my existing rear running lights/brake lights/turn signals to LED, I am using only a fraction of the power previously needed on the rear circuit. I could add a large array for a 3rd brake light and still be using less power. No relay needed. Plus I am putting out considerably more light than before...

Here's a picture. Left is a standard bulb, right is LED.


Geoffrey M Baker

Watch the LEDs for burnout. I've had 3 3rd brake lights in my hot rod 'cause they do take a dump on occasion.

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MAndrus

I think they've been there about 5 years now, no problems. They are rated for far longer than incandescents. Certainly, they can burn out (100,000 hours average, though, compared to just a few thousand for incandescents).
I've had poorly made cheap plug-in led bulbs burn out, so I would recommend avoiding the junk ones at Pepboys etc.
I built my own using solid state high power LED dies plus appropriate drivers, all heatsinked. You can find the thread by searching on "LED".
Much brighter than standard, on average far more durable, and they use far less power. Hard to beat.
Geoffrey M Baker

This thread was discussed between 19/07/2015 and 21/07/2015

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