Brake light switch - Repeated failure

J

John Larkin

Member
The brake light switch on my car (1974 P6B automatic) keeps failing. I am renewing the switch every nine to ten months. I use a new original Lucas switch each time. Has anyone else experienced this problem --- and found a cure?
 
My brand new brake light switch, installed six days ago, has failed. This was the last of three brand new Lucas items that I bought about ten months ago here in Dublin. I bought at least half a dozen from UK suppliers previously over the last four or five years. Why do they keep failing?

I despair. I'm going to install a mechanical switch.
 
Hi

are they failing electrically or hydraulically?

Have you any extra brake lights fitted? if so it could be overloaded electrically.
 
The switches just fail to close the electrical circuit. If I detach the two wires and touch them together the brakes lights come on. I have never tried to open up a failed switch as they are of bonded metal/plastic construction, but I would guess that they have a diaphragm that moves under pressure of brake fluid and so makes the electrical connection. No switch has ever leaked brake fluid. My car's electrical system is standard.

JL
 
Interesting, the switch is a standard item used on many makes, wonder if you have managed to get a bad batch. The only time I have blown a brake lamp switch was descending a steep hill with a caravan, car was an auto so prolonged braking fried the switch, twice the number of brake lights because of the caravan. The genuine fit Rover tow bar kit includes a relay for the brake lights so it looks as though the switches don't have a lot of spare capacity.
 
Thanks for the feedback necpwa.

I'm going to try out a standard brake light switch once more in conjunction with a relay to carry the current to the brake lights.

JL
 
hi john
just a thought but have you checked the stop/tail light bulbs.
they may be the wrong voltage/wattage for your car.
they should be 12v 5/21w
in all the years i have been in the trade and have owned a p6 i have only had one go faulty (lights stayed on all the time)so i would be amazed if it was the switch
nick
 
I checkd the bulbs and they are right. I'm installing a new switch tomorrow, along with a relay to make life easy for the switch.

I cannot recall this type of failure happening at any time during the 1980s. It seems to have started within the last five years or so. If I discover anything interesting I'll post it in the forum.

Thanks to those who responded.

JL
 
Brake light switch repeated failures:
Have you checked the cleanliness of the brake fluid? If you have internal silt (fine rust powder) it may be plugging your hydraulic brake switch orifice ;-)

Drain the brake fluid, put fresh stuff in the reservoir, and pump the pedal while draining out each front brake caliper and the rear caliper before installing your switch. Rebleed and you are good to go.

Eric from the colonies
 
Brake fluid is clean --- it's renewed every 15,000 miles. I'm going to try to open up the latest failed switch and see what went wrong inside.
 
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