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MG TD TF 1500 - Brake light again

Hi Folks,
Some one year ago I modified my brake light system as described in ttalk:

At the same time I changed to DOT5 brake fluid but I stay with the old brake switch.

Unfortunately, now I have the Problem that the brake light burns permanent. How can I check if it is the hydraulic operated switch or is it the relay?

In case the hydraulic operated brake switch has to replace must I bleed the system or must I change the brake fluid completely?

Thanks for your help.

Hi Guenther,
a couple of weeks ago I had the same issue. I jacked the car a bit and disconnected the wire from the switch to the relay (easy, just one tiny screw) and than connected a Ohm meter to the two connecting points at the switch. And they showed that the switch was closing constantly.
At a normal carparts shop they sell a hydraulic switch marked KW 03.3005 for 9 euro. A switch that still is in use for youngtimers Fiat and Alfa and others.
I unscrewd the switch, hold the hole with my thumb and quickly screw in the new one. Not much DOT5 came out but I did the de-air procedure for the rear brakes.
The new switch has blade contacts instead of the screwing ones, so you will need two blades and a tool to put them on. Greetings, Huib
Huib Bruijstens

No need to bleed the brakes after replacing the switch as long as you are relatively quick about getting the new switch in place. Since the master cylinder is higher than the switch (by a small amount) you will just dribble fluid out but won't ingest any air. Cheers - Dave
David DuBois

Hi Guenter

Just disconnect the switch and if the brake lights remain on your relay must be faulty, if the brake lights go out, then the switch is faulty. I obtained a new switch a few months ago from a UK supplier on ebay, it has the screw terminals. I have also installed the relay and had no problems so far. Matt
Matt Davis

Hi Matt, any idea oft the name of the supplier? I like the screw terminals.
Thank you

I found a swich on Ebay 360250020473 but no information concerning the thread.
It is mentioned that it will fit for MGA all years. Will it fitt to the TD as well?


The switch I bought is ebay item 190539962602 it fitted perfectly and was one of the few joints which did not leak after I filled the system with DOT5! It has only been in place for about 2 months, so I can't confirm how long it is likely to last, but it looks well made.
Matt Davis

I once suffered continually lit brake lights on my TD so I assumed the switch was stuck on and purchased a new switch.

It turned out that my (recently replaced) master cylinder was not properly relieving pressure. After about every dozen steps on the brakes, the lights would stay on because the brake hydraulics remained pressurized.

Have you checked your master cylinder?

Mark Sherman
Mark A. Sherman

This thread was discussed between 13/06/2011 and 14/06/2011

MG TD TF 1500 index

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