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MG TD TF 1500 - Brake light switch on pedal

I installed a high third brake light and drove about 200 miles this past weekend. With the third light I can see in the mirror the glow letting me know that the light has been turned on. The problem is with the brake line pressure switch the light doesn't glow until I really press hard on the pedal. I rarely apply the brakes that hard so most of the time I'm not getting any brake lights. I'd like for the lights to come on when I do not much more than look at the pedal.


Has anyone installed a limit switch on their brake pedal to control the brake lights?


(1) where did you get the switch?

(2) where and how did you mount the switch so depressing the pedal activates the lights?


Thanks all for your help.

Jud
'53 TD 25009
J. K. Chapin

Jud, any decent brake light switch should work properly. Try a new switch. Go to your neighborhood NAPA and get an SL144. Your name seems to show up on threads about brake light problems. Do you have some sort of non-ordinary plumbing? Bud
Bud Krueger

I've been using the Ron Francis Wiring low pressure switch which comes on at just a touch of the pedal. When working it's fine but I have experienced failures of even these supposedly heavy duty switches. In a conversation with the tech rep from Ron Francis I was told that the switch is acceptable with standard incandescent bulbs but no extra bulbs in the circuit. Also halogen bulbs overload the switch and cause failures over time. I was advised the only solution is a relay where the switch operates only the relay, not the bulbs. I was also thinking that cars with the turn signal relay may also contribute to extra load.
John Quilter (TD8986)

A relay in the brake light circuit will correct the problem. I provide a relay/arc suppression circuit that is installed between the brake light switch and the brake light that keeps the brake light switch from dying over short periods of time. If you are interested in one of the brake light relays, contact me at SUfuelpumps@donobi.net Cheers,
DW DuBois

I had dim rear brake lights until I installed Dave Ds relay 3 years ago, the lights are now brighter than ever! Perfect instructions, very easy hook up. Thanks Dave, PJ
PJ Jennings

Bud, so far as I can tell, my brake plumbing and brake light wiring is standard. The only thing I've done is to tap into the left brake light wire to power the third light. The third light comes on with the factory brake lights and blinks when I give a left turn signal. I know the blinking on left turn is non-standard but it's OK by me. I'll go get a NAPA SL144 and try that.

Dave, you have mail.

Thanks.

Jud

J. K. Chapin

As an aside, I went to NAPA last weekend to get a new bulb for the front right turn signal/marker light and fount that although the diameter of the bulb's base fits the socket, the pins for the bayonet socket are not the same as what I took out. The new pins are offset - one close to the bottom of the base and one about midway up the base. To use it we simply filed off the midway pin. I suspect, but don't know, that this is the same bulb as used in the brake/tail lights. Do the usual suppliers (Moss, ABS, etc.) sell bulbs with the correct pin placement?

I did notice that the single filament bulbs seemed to have the necessary pin placement with both pins close to the bottom (i.e., close to the contact points) end of the base.

Thanks

Jud
J. K. Chapin

The offset pins were designed that way to prevent the bulb from being inserted incorrectly. I believe the reproduction taillight based all have the offset pins to work with modern bulbs. They are easier to obtain and less expensive as well. The plus side also s that you can easily install LED bulbs from your local parts house at a fraction of the cost of parallel pin bulbs

Bill Chasser
TD-4834
W A Chasser

If you have turn signals the front bulb has parallel pins with 5/21W power. Trial and error is the way to install. You have a 50/50 chance of getting it right first time.

The rear have offset pins in 5/21W power.

Peter
P G Gilvarry

I replaced my rear/brake light bulbs with dual ’fillament’ LED versions. They have offset pegs. I was developing a new wiring harness as I was adding separate turn signals so adding an extra lead for the brakes was no problem. I am assuming that with LEDs there is no need for a relay.
Chris
C I Twidle

No need for a relay with LEDs, which is what I have done. I also added an LED high level brake light.
Dave H
Dave Hill

Jud, your problem is not unusual. I had the same thing happen to the NAPA switch on my TD I had. It took full panic stop mode to activate the switch.

I replaced it with another switch which at least solved the problem until I sold the car. Dave suggests
wiring it through a relay to prevent the arcing inside of the switch points which may lengthen the life of the switch.

As for the mechanical switch.... Most operate as a normally open switch... in other words the circuit is broken until you touch the pedal....same as the hydraulic switch. They are usually touching a facing side of the pedal arm and with the T type it gives you two choices of mounting the switch. One would be in the pedal box and while we know what a pain the box is, that would probably be the best area to try and mount one if you are truely serious about tackling the job. I don't see mounting one inside the foot well as really feasible as any mounting would interfer with the pedal operation.

There would be two possible mounting locations for the switch. One is above the the pedal shaft so the switch closes as the brake pedal arm moves away. I do not believe that there is enough room above the master cylinder to make that happen. The other area would be the front of the pedal box and below the pedal shaft. I think this might actually be do able. You would have to drill a hole in the front face of the pedal box. I think I would try and center the hole to match one of the faces of the yoke and have the switch touch that point. The switch would have to have a fairly long barrel of threads I would think to reach the face of the yoke. You would then have to weld a nut to the out side of the pedal box face and use a locking nut with it to secure the switch. Similar to the way the switch works on an MGB.

As for the bulb NAPA gave you. It was the wrong one. They need the correct number which they may have not had in stock but can certainly get from the warehouse.


L E D LaVerne

Dave DuBois, You have mail.

John Quilter
John Quilter (TD8986)

Laverne, thanks. I just bought a new NAPA switch that I hope to install this weekend (or maybe next week end, you know how that goes) and I'll let you know how it goes. If I go with a mechanical switch I may try a limit switch with a roller on the end of a lever arm. These types of switches used to be readily available at Radio Shack but I suppose they are still available from somewhere.

Jud

ps: I've always been concerned about having the lift pad under the pedal box but it appears that you do it with no adverse effects.
J. K. Chapin

My early pedal box was once used for lifting the car. It took a good bit of prying to take the dent out so that I could get Declan's Rose-joint clutch linkage system to work. LED's large area rubber pad would probably get around that. Bud
Bud Krueger

Well DUH!! My buddy and I decided to install the new NAPA brake light switch. After putting the car on the lift we disconnected the two wires and decided, just for the heck of it, to test the old switch before taking it out. We discovered that just light pressure on the pedal closed the switch (the old switch is also a NAPA SL144 about five years old). We also discovered that we were getting only 5 or less volts at the end of the wire (and then 12.5 and then 5 and so on with no repeatable pattern). After fiddling with a bunch of perfectly good connections we finally discovered that the ground strap to the battery was loose on the battery terminal. Tightened it up and now all is well.

Drove 200 miles last Saturday and noticed an intermittent engine skip that I was going to see if I could track down. Now I'm wondering if the loose ground was causing the skip. Aw shucks, now I'll have to take it out on another beautiful fall day and see if the skip has gone away.


Dave, at the moment it ain't broke so I'm going to defer on installing a relay but thanks.


Jud
J. K. Chapin

Good to hear it, Jud. Should have been fun trying to drive with the headlights on. Bud
Bud Krueger

Jud,
A couple of weeks ago I had an intermittent misfire. After testing all the ignition components I found it was only a bad fuse connection, a quick clean with emery cured it.
It was the same as yours, as soon as a load was applied the voltage dropped off.I had only been checking the voltage with the ignition off!!!!
Ray TF 2884
Ray Lee

There is a voltage sensitive LED out there, from the UK. Stick one of those in your line of sight, Connecticut it to the A4 terminal of the fuse box and ground and you have an immediate picture of "how-goes-it" on battery and charging condition.

Very cheap too.

Peter
P G Gilvarry

Here is the link:

http://www.sparkbright.co.uk/sparkbright-eclipse-battery-voltage-monitor.php

Peter
P G Gilvarry

I wonder if that Sparkbright would fit and replace where the ignition light is in the instrument cluster.

Jud
J. K. Chapin

This thread was discussed between 14/10/2018 and 20/10/2018

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