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Brake lights not working?


richard lane

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What Titanium7 says, as the best place to start.

It's often possible to fix this without replacing anything. Don't take the switch apart until you've found the notes in the archives... there's a spring which tends to make a break for the Swiss border...

Do you have a multimeter already?

Jonathan

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Easy to fix. Take off top cover of pedal box. Prise end cap off switch carefully and catch the spring inside. Pull out brass piece and squeeze the two legs together a bit, cleaning off any grease that is on the contact part at the end. Reassemble and test. Note spring only fits one way round. If you lost it on opening switch .... hunt for it all day.
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Hi guys,

Thanks for all the help!

Opened up pedal box, and took switch out which was actually quite loose as the retaining screws seemed a bit loose.

Anyway it is the switch as it was working on and off as I was playing with. Put it all back together 

and seems to be all okay.

I do not have a multimeter so obviously need to invest in one!

Thanks again for the speedy help!

Cheers Rich

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  • 5 years later...

Resurrecting an older thread...   my brake lights have stopped working, 2 weeks after the MOT :-( 

 

I have taken out the switch, disassembled and cleaned it per the steps above but still no worky.

I then put a test light (one of those screwdriver/probe type things with a small crocodile clip at one end and a probe at the other) connecting the 2 wires and it lights up. However the brake lights don't come on when the test light/probe is connected - whether the pedal is depressed or not. 

 

Would you expect the brake lights to come on when the 2 wires are connected with a probe and the brake pedal depressed (or not)?

 

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"Would you expect the brake lights to come on when the 2 wires are connected with a probe and the brake pedal depressed (or not)?"

Yes. But you don't need the probe for that: the brake lights should come on when you short the two sides of the switch together (with the ignition on).

It sounds as if one side of the switch is live, but I don't know what your probe does, so if in any doubt check the brake light fuse.

Any recent work or other problems, and are all the other lights working?

Have you got a multimeter, and would you like a wiring diagram?

Jonathan

 

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You'll only need a couple of functions of the multimeter: checking for whether a point of interest is live compared to a good earth, and checking for continuity of a circuit. 

Let's do this one step at a time, but do you have the wiring diagram for your Seven?

Any recent work or other problems, and are all the other lights working?

Jonathan

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Really appreciate your help Jonathan!  

 

The brake lights weren't working when I got the car 4 months ago, so I checked all the fuses in the fuse panel (all ok), removed the boot floor, cleaned up all the connections, removed the light lenses and bulbs, made sure they were all clean etc and they started working. 

Since then, I had the LED Lifeline high-level rain light wired in (by a Caterham specialist) to the brake lights while the car was in for a service, in order to turn it into a high-level LED brake light. 

 

The brake lights have worked fine since then, but stopped working sometime this week (I don't know exactly when, as I just noticed them last night). 

 

I don't have a wiring diagram for my car but would appreciate one. Mine is a 2015 ex Academy car (Ti-VCT Sigma). 

 

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I take it the bulbs are ok?

Is your high-level brake light connected into the brake-light circuit via a special loom (like this)?  If so, check that the connectors are firm and that the terminals inside are properly aligned.  Sometimes they can become dislodged, with a resultant poor contact.

JV

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I've just been out to check all the fuses in the panel (removing them 1 by 1) - all are ok. 

 

I've removed the boot floor, disconnected the multiplugs for each rear light cluster, visually checked for anything burnt/corroded (all ok), then sprayed a little WD40 into each side and reattached. 

Still nothing.... 

I'll check the bulbs and clutch split pin in the morning light, and will double-check the subloom for the Lifeline high-level rain light. 

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I can't thank Jonathan Kay enough for his help in diagnosing the problem. As BC was ‘down’ this morning we communicated via email, but I have posted Jonathan's and my conversation below for future reference - in the hope that this may of help in future to people who, like me, are complete numpties when it comes to electrics!

 

Jonathan advised using a multimeter to test the brake light switch. I was gifted a multimeter some time ago but (shamefully) I didn’t even know how to work it!  Before you all laugh, I’m ok mechanically… I’ve taken engines, gearboxes, suspension, diffs and all manner of things apart and rebuilt them, I even built a Land Rover Defender 90 from scratch - every single nut and bolt -  20 years ago. But when it comes to electrics, I’m completely lost, it’s always been a black art to me.

 

My email provider has somehow lost Jonathan’s first email, but he told me to turn the multimeter to any setting that measured voltage, put the red probe on the positive battery terminal and the black one on the negative and see if it read anything like 12v-13v. It did. 

Then to do the same at the brake light switch (jam a probe into each side terminal and see what it read). 

 

 

 

Morning Jonathan, 

I’ve done as you said and used the multimeter. On the battery it read 12.85 and at the brake light switch with the probes jammed into the terminals it reads 12.34v - very slightly lower than the reading at the battery. 

IMG_1960.thumb.JPG.7048b358ad991d8b35cdf43c669a830f.JPG

I’ve taken the bulbs out and they look fine. 

I cleaned up the Earth on the inside of each light cluster but they weren’t bad, I only did so because I hear 99% of all problems are earth related.

Still no joy. 

-S

 

 

 

OK… the multimeter is working and you’ve got the right range.

Put the black probe on the battery negative terminal and keep it there.

Then the red probe on one side of the switch: what voltage does it show?

Then the red probe on the other side of the switch: what voltage does it show?

And what colours are the wires on each side of the switch?

The ignition needs to be ON for this test.

-J

 

 

 

Okay, with the ignition on and doing as you’ve described the multi meter reads 12.22 when the probe is on the side with the 2 wires (red wire +  plain green wire)  

It reads nothing at all with the probe on the side with the single green wire with purple stripe. 

IMG_1965.thumb.JPG.36fdee6b18720939fc8de81ae00e69e6.JPG

-S

 

 

 

You now know the input and output side of the switch and that it has a live feed at the input side.

Green is the ignition-switched feed, and Green/ Purple goes from the switch to the lights. I don’t know what the red wire is.

With the ignition ON:

Leave the black probe on the battery negative. 

Put the red probe on the OUTPUT side of the switch. 

Press the switch fully in by hand.

What happens to the voltage at the OUTPUT side of the switch?

And while you’re doing that see if the brake lights are coming on when you press the switch fully in by hand.

-J

 

 

 

Jonathan, you really are teaching a man how to fish rather than giving him a fish. This is hugely appreciated! 

So, doing what you say, with the red probe on the output side of the switch and the black probe on the battery negative terminal, when depressing the plunger on the brake switch nothing at all happens to the voltage - it just says 0.00. 

Also, when pressing the switch nothing happens at the lights.

-S

 

 

That’s the idea!

Sounds as if the switch is bust.

To confirm that now switch the multimeter to a resistance range, one in the section with an Ω.

Touch the two probes together and it will show the low resistance and continuity. Then do the same on any piece of bare metal so that you’re familiar with the response.

Disconnect all the wires from the switch

Check that you get continuity when you put both probes on the same side of the switch terminal

Now put one probe on one of the switch terminals and one on the other.

On a working switch there’ll be no continuity until you press the switch in and then there will be… what happens on yours?

-J

 

 

 

So when I do that the multimeter shows the number 1 when the probes aren’t connected to anything. 

When I touch the ends of the probes together the numbers change rapidly and then settle to 001.  Is that correct?

I am a complete moron and I don’t know what continuity is, but when I do as you say and put both probes on one terminal on one side of the brake light switch the same thing happens, i.e. the numbers fluctuate and then settle down to 001. This is the same for both terminals i.e. on each side of the brake light switch.

 

IMG_1970.thumb.JPG.cccabe15e7fd358b988b9986fe8ff055.JPG

 

 

 

Re your last paragraph, when I put a probe on each terminal on the switch the multimeter reads the number 1 and when I press the plunger on the switch it stays the same, nothing happens, it still reads the number 1. 

IMG_1968.thumb.JPG.f0cd7452fc2d891216ecfaae6475fae5.JPG

 

-S

 

 

You’re doing it right.

That 1 means high resistance/ open circuit/ no continuity.

That .001 means low resistance/ good continuity.

Nothing happening to continuity when the switch is pressed in confirms that the switch isn’t working.

Please see next email.

-J

 

 

 

It’s common for these switches to fail.

A better model is available:

https://www.lotus7.club/forum/techtalk/brake-light-switch-14

 

But it might be mendable. You can take them apart and have a look, but BEWARE… there is a little spring that makes a bid for freedom when you open the switch, so this needs to be done deep in a box. Same thread as above:

https://www.lotus7.club/forum/techtalk/brake-light-switch-14

 

-J

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Fixing the CC brake light switch is a 5 minute job. The spring isnt that ferocious at all, just prise end cap out gently and keep your hand over to restrain the small spring. You'll find a u-shaped contact inside ... the legs just need squeezing together a little. Clean any greasy gunk off them.
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"I’ve taken the bulbs out and they look fine"  Obviously not the issue in this case as the fault has been found but a broken bulb is not always obvious to the eye if the filament has broken due to a knock or similar.  Better to check by connecting to a known good supply, e.g. the battery

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