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MG TD TF 1500 - How to wire up a third brake light

Hi
Can someone help me with an electrical issue? I have a nice third brake light for my TF, to be mounted high. Has two wires, one ground of course.
How is the best way to wire it up? I thought I could figure it out, but spent an hour or two and could not.
Thank you.

Tom
T Norby

One wire goes to ground and the other wire can be spliced in to the liscence plate light (red?)
Sandy
ss sanders

Check it out but I think there may be three connections.
The ground could be the frame of the light. If so wherever you mount it you must insure the frame is at electrical ground.

I would believe the two wires go to two separate filaments in a common bulb.

(Just look at the bulb. Does it have two solder blobs or one blob?).

If two, one wire goes to the license plate as Sandy noted. The other should go to one of the brake lights, the filament that glows when you step on the break.

You could run both wires to a break light. The break light should have two wires coming out also, with the frame as ground.

Now a complicating issue is that if you do have a two filament bulb there is a bright filament and a not so bright filament.

The Bright filament on your third light should be lit when you step on the breaks.

One simple way to hook it in is to extend the wires to the taillights, add bullet connectors and purchase some 4-way connectors from Moss.

If the bulb only has one solder blob then the hot wire should go to the stop light filament on the taillight and the other would be ground.

Another place to pick up the stop light circuit is on the break light switch, under the car, just aft of the master cylinder

Jim B.
JA Benjamin

Thank guys. So fast!
This is a single filament bulb. It will be a brake light only. Sandy, I don't understand how I could get brake light action from the license plate lamp.
Jim, you mention going to the switch aft of the master cylinder. So, I can do that? The wiring diagram shows those wires going to the relay. I was worried I would damage something. So, the one red wire to the switch, the ground to the frame somewhere, correct?

Tom
T Norby

Yes. You can go to the break light switch.

You do not need to go to the relay since the center light is not involved in the directionals.

In fact now that you mention it, the break light is the best place to pick the light up since you do not want it flashing.



Jim B.
JA Benjamin

Tom, apparently you're talking about an incandescent lamp and not an LED. That simplifies it. Check the wiring by touching one wire to one side of your battery and the other wire to the other side. If it lights you're ready to go. Tie one of the wires to ground. Yes, the brake light switch is the place to connect the ungrounded wire. Under the car, at the stop light switch you should find a green with purple wire. That's the one that you want to piggyback onto. When you start testing don't forget that the ignition key must be ON for the brake light to come on. Bud
Bud Krueger

Thanks Bud
Yes, incancescent light. Old school. I will get this done tomorrow.

Tom
T Norby

OK, I got it done. Here is a photo of how it looks. My TF already had a Lucas 494 reverse light on the rear valance. I like how they look. I bought a repro 494 light with red lens on e bey. You may have seen them. I found the quality and finish to be very good and the price was modest. Now I have a matching set of 494's.
It lights only for braking. Single fillament bulb. That is want I wanted. I mounted it with the fog lamp mount bracket that Moss sells. Fit nicely to my luggage rack. I have bullet connecters up top, so I could easily remove it if I wanted an original look.

Tom
'54 TF


T Norby

This thread was discussed on 28/09/2014

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