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MG TD TF 1500 - Third brake light

I just added a (Moss Motors) third brake light.
It is well mounted, but I am having problems hooking it up.
Since the tail lights are so dim, I decided to just hook it up as a third tail light - to go one with the tail lights.
I tried hooking it into to left tail light and then to the license plate light.
In each case after about 10 seconds of connection the light to which it was attached went out as well as the third light.
When I disconnected the extra light, after about 60 seconds the original light came back on.
Any suggestions?
I think I will connect it directly to the battery with a separate switch.
Thanks,
Billl
W Chandler

Sounds like the flasher can or (if you have one) a confused relay. I thought I was hooking mine to just the brake light circuit but ended up hooking it up to the brake/turn signal circuit. Since mine is over the tag on the left side that's OK - it comes on with the brakes and flashes with the left turn signal.

Jud
J K Chapin

Something's not right, Bill. Looking at the Moss ad for their Item #116-115 I see that it says "Negative ground only". It's obviously an LED device. I'm curious about the grounding. Is there just a single wire coming out of the unit to be connected to the light circuit? Does it depend upon a mechanical connection to a good ground? How did you ground the light kit? Bud
Bud Krueger

Bud and Jud,
Thank you for your comments.
There are 2 wires coming out of the unit.
I could not see anything in the ad that said negative ground only.
When I connect it directly to the battery, red wire to the + terminal (ground) and black wire to the - terminal, it lights up fine. If I reverse the wires it does not light up at all.
Since on both test occasions (tail light and license light) I used the regular lighting system and not the stop light, I wonder if it draws too much current for those systems. Since the brake light is much larger, it might tolerate this extra draw on the current. Unfortunately I know very little about electricity.......
On each of the test occasions I connected the red wire to the "ground wire" for the light and the black to the other wire. It would work well for a brief time then both lights would stop working.

If I hook it directly to the battery with a small switch under the dash, it should work fine by not using any existing circuit.

My concern with the lighting is not so much the brake lights (they are actually very bright), but with the tail lights which are very tiny and dim on a 53 TD.

Many thanks,
Bill
W Chandler

What voltage do you measure at the rear light?

Maybe your brakelight switch doesn't make proper contact,or the earthing of the lights is bad, thus causing dim original brakelights and failing alltogether with the added current drawn by the third light?

If the voltage is correct, maybe switching all the lights via a modern relay is a solution?
Willem van der Veer

Bill, what's the Moss part number of the light? I can't understand why Moss would say "Negative ground only" in their ad if both wires are available. Do you have the ability to measure the current draw of the light? Bud
Bud Krueger

If I understand your proposal correctly, you'd flick on the wwitch to have the third light illuminate continuously as a tail light. I think modern drivrers would mistake that for a brake light and fail to notice when the actual brake lights came on. I believe that you are better served to sort it out and have the third light operated in conjunction with the brake light circuit.

I'm assuming that you purchased the Moss 116-115. I looked it up and it has, as you said, a red and a black wire. So long as the body of the fixture is insulated from the wiring and lighting circuit this fixture should work with either positive or negatice ground. For positive ground, as you said, red to car frame (+) and black to the wire that makes the brake lights come on (-). Mine is not from Moss (mine's a cheapo from Advance Auto) but that's hw it works and it draws negligible current (a quick Yahoo search indicates that red LED draw between 20mA [model railroad) and 150mA [decorative house lighting] so your 20 LED array should not draw more that about 3 amps).

If it works connected directly to the battery but fails at the back of the car it seems that something is amiss between the battery and the back of the car. About all there are to go bad are the brake switch, the wiring and the frame ground. I'd keep plugging away at those. Maybe you could try running a temporary new wire to the lights to ensure that the existing wires are not the problem.

Jud
J K Chapin

Connect it with a direkt wire from the brakelight switch to the third brake light.

Klaus
Klaus Harthof

If you mean hook it up to the tail lights, and not the brake light, I think its a real bad idea. The logic behind a third brake light is that studies have shown that drivers following another car tend to focus on the upper center of the car ahead, and will respond measurably more quickly to a brake light located there than ones off to the side.

Putting a tail light there, where people expect to see a brake light, could have a reverse effect, lulling them in effect into thinking everything is well as long as the 3rd light remains constantly lit, and hence actually delaying their reaction to the brakelights on the sides.
kylemorley

Bud- This is the item from Moss Motors. It does have two wires. See attached image.
Bill

W Chandler

Klaus,
I took your advice and connected this third brake light directly to the brake light switch and it works perfectly. I just grounded the red wire from the light and connected the other to the down side of the switch and when the switch is connected by stepping on the brake pedal - the stop lights as well as the new third light are all lighting up.

The new third light is the horizontal bar just below the MG logo on the spare hub cap. It is attached to a new metal bar which is attached to the metal that holds the license light.
(Image attached)

I also took everyone's advice and will use this as a Brake Light and not as a running light.

Thank you all for your advice.

Bill Chandler
Ann Arbor, Michigan

W Chandler

Sounds like the way it should be working, Bill. Good job. Question now is why Moss is saying "Negative ground only"? Bud
Bud Krueger


Maybe it's made of governmentium and they didn't want to chance confusing the "lepton-like particles called peons"

http://www2.mg-cars.org.uk/cgi-bin/or17?runprog=mgbbs&access=&mode=archiveth&subject=8&subjectar=8&thread=201310211254278790

Jud
J K Chapin

Hi Bill,
What I really mean is an additional wire to the third brake light.

For those who have wire wheels I send pics from my solution:

Klaus Harthof

Pic with wheel at daytlight

Klaus Harthof

Brakelights when it is dark.

Kind regards
Klaus

Klaus Harthof

Klaus, thanks for the helpful photos. I will try to take some photos after dark tonight to see how mine looks. I will post soon.
Your third brake light is impressively bright and well cleverly hidden.
Bill
W Chandler

Klaus,

I like your solution and will likely do something similar on mine.

I see what appears like 2 holes on the upper side of the spare mounting. Did it not work there? Is there a reason you mounted it low?

Jim
J E Carroll

Jim,
at first I mounted the brake light on the high position. Therefor the two holes in the hight. But we like to travel for longer times so we had to take much luggage (especially for my wife: shoes, Dresses etc) So I found a solution to folder the side wings into a small bag and I put it on the spare wheel. see pic. (So we have more place behind the seats.)That's the reason why I mounted the brakelight below.

If someone is interested how to fold the side wings to a small place, I make a new thread.

Klaus

Klaus Harthof

I have attached a photo with and without the third brake light. This clearly makes the car safer. I will also try to attach one in the daylight so you can see the small profile of the Moss LED light.
I think it will take three submissions for these. The first is obviously with the third light on.
Bill
Ann Arbor, MI

W Chandler

With the third light covered.

W Chandler

The photo of the third light is in a comment above, but I will resend it here.
It does have a very small profile and is a very solid chrome.
Bill

W Chandler

This thread was discussed between 11/11/2013 and 16/11/2013

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