mk1-forum.net

Hi all as the title suggests my brakes lights are staying on, would this be a faulty brake pressure switch or should I be looking at wiring problems. Most posts I've read on faulty switches are when the brake lights don't work, whereas mine won't stop working. Thanks in advance, cheers Tim

You did not say if this is a pedal actuated switch or hydraulic switch.

If this is a pedal actuated switch, start at the pedal. Make sure the switch is adjusted correctly. The switch is a normally closed type (brake lights on). When the pedal is at the top of its travel it depresses the switch plunger and holds the contacts "open". When the pedal is depressed, the switch plunger moves back out so the contacts close. If the switch appears to be adjusted correctly, disconnect the wires to confirm that the lights go out.

If this is a hydraulic switch, disconnect the wires at the switch to confirm that the lights go out.

In either case, if the lights don't go out with the wires disconnected from the switch you may be dealing with a parasitic ground problem where an unrelated (but peripherally connected) circuit is feeding the brake lights.

Yeah as above is a great guide. Any other electrical issues with the car?

Thanks for rapid response guys. Its a hydro switch and yes lights go out when both wires disconnected.So this would indicate a faulty switch then.thanks Tim

sometimes pouring a kettle of red hot water over the hydraulic switch and pumping the pedal will help free it up

the little plunger inside sticks and the hot water shocks it all back into life.


doesn't always work, but its worth a quick go!

If Rich's method does not address the problem then repair is by replacement.

That said, IF you have converted to DOT-5 fluid from DOT-4, you will be better served by installing a pedal actuated switch and running wires from it to the ones that formerly were connected to the hydraulic switch. The hydraulic switches do not like DOT-5.

If replacing the switch, the Hella ones are the go, many others seem to have very poor life

I trust the wires are on the right way......

Thanks all for your replys. The switch looks to be original to car,but I,ve not used it for a couple of months so maybe the hot water trick may kick it back into life . Thanks for all your advice, Tim

bpirie1000 wrote:I trust the wires are on the right way......

It don't matter...........

many years ago the local garage collected my mk1 from work and took it away for an mot.

after a while it came back and it had 'only' failed on no brake lights.

the tester wasn't happy as he had nearly got into fisticuffs with some bloke who had nearly rude-boyed him at a roundabout......

that's when the lack of brake lights had first been noticed!

apparently it had been a proper road rage argument with both of them out the cars and screaming at each other


they wouldn't collect any of my cars after that and I had to start using another garage........................

Rich, did someone catch it on youtube?

dklawson wrote:The hydraulic switches do not like DOT-5.

Doug, Please enlighten me!

My Marcos has always had DOT5 and I have always had brake switch problems...
What's up with this combination?

I've often thought about putting a mechanical switch in, but I don't fancy the
job of taking the MK1 style pedal box out to make the appropriate mounting
holes.

Another "MOT story":
Brake lights OK before I went, but then failed - I had to get it fixed within
24 hours or pay again so I had to come up with a cunning plan!

As a "quick fix" (Bodge), I cable-tied an old motorbike pull-type switch to the
steering column. One of those long springs out of a washing machine was
hooked behind the pedal and the other end through the eye of the switch...
Suitable wires poked through the vent pipe to end up in the original location,
Job Done!

Ian

Spider wrote:Rich, did someone catch it on youtube?

no thank god...

but it did happen on 'crash roundabout' in Harrogate, which people round here know is some sort of crash vortex that catches the un-worldly out (normally old ladies, or people who don't live round here)

there are endless crashes there and quite often on the way home I will see a car with no front end, or one that's been comprehensively 'rude-boyd' by some old dear not looking where she is going!


the best one I ever saw was an old lady who had buried her car into the side of a bus that she 'didn't see'..................

ianh1968 wrote:

dklawson wrote:The hydraulic switches do not like DOT-5.

Doug, Please enlighten me!
Ian

I don't know the physics or chemistry that is at work but many BMC cars of the period used hydraulic brake light switches. There are tons of reports online of these switches failing once the switch is made to DOT-5. The failures occur not just for the old switch that has been exposed to DOT-4 but to the replacement switch that has only been used with DOT-5. The majority of switches just seem to fail after exposure to DOT-5 for a few weeks.

On some forums I have seen references to a Harley-Davidson hydraulic brake light switch that has been used with success but I have not tried it. I do have DOT-5 fluid in my Mini and after its switch failed I installed an industrial Micro-Switch on the pedal box. This conversion was only going to be a stopgap change until I found a working hydraulic switch. The Micro-Switch has been in place for about 12 years now. It's not pretty. I only mounted it with one screw and bent the arm of the switch to get the trip adjustment I needed.

dklawson wrote:
On some forums I have seen references to a Harley-Davidson hydraulic brake light switch that has been used with success .

I would have thought that a Harley Davidson switch will just drip fluid from new............

rich@minispares.com wrote:I would have thought that a Harley Davidson switch will just drip fluid from new............

Nyuck, nyuck, nyuck! I'm not motorcycle guy but I understand "new" Harleys are a lot more reliable than older models. Regardless, I think the cars from BMC and Triumph have more of a reputation for marking their spots more than Harleys!

On a complete tangent, I used to have a steady stream of Harley owners coming to the shop to buy HIF44's. Apparently the standard carb was crap.

nick rogers wrote:On a complete tangent, I used to have a steady stream of Harley owners coming to the shop to buy HIF44's. Apparently the standard carb was crap.

oddly enough, so do we

they also like the su ram stacks we sell.

I even sold a Austin cooper s boot 'S' to one guy so he could fit it to his sportster

dklawson wrote:

ianh1968 wrote:

dklawson wrote:The hydraulic switches do not like DOT-5.

Doug, Please enlighten me!
Ian

I don't know the physics or chemistry that is at work ....

Fluids - especially fuels and oils - will swell rubber and plastic materials to some extent, sometimes causing complete liquefaction.

In some cases a little swelling is a good thing eg O rings swelling in their housing giving a better seal.

The original BMC components will have been designed to cope with the fluids of the era.

All the changes to modern brake fluids, bio fuels and antifreezes mean that 1950s spec rubber are not suitable anymore.

A common example of this effect is the ethanol (which is in all petrol now) causing swelling and break down of the flexible hose from chassis to carb.