Brake light switch

[Ufudu]

I had a comment today from a friend who followed me whilst I was driving the Morris saying the brake lights were not working.

Checking the lights I noticed that the "brightness" depends on the brake pedal pressure, obviously the sensor switch contacts are pressure dependent. Also you need a fair pressure to get full brightness, and I generally drive with a light foot on the brake, using the engine to slow on corners, so the lights may not be coming on at all.

The switch is a new "Lucas" from ESM but I am aware of the comments from others that there is a bad batch out there.

So, I first will have a go at augmenting the pressure switch with a relay that will eliminate the variable brightness (since I am not particularly keen on breaking the hydraulic seal & trying another switch that I don't have).

My question is, I seem to recall a topic where a member added a mechanical microswitch to the pedal itself, to get brake lights activated with only little movement of the pedal. Does anyone recall this?

thanks

Erwin

[Ufudu]

Ah. I think I have found it.

http://www.mmoc.org.uk/viewtopic.php?f= ... ch#p473430

I should use the search function first I guess

[Roni]

A relay to the existing switch works too if it functions. I had a problem with mine, it was only passing 10v to the brake lights and therefore were not bright enough to be legal.

[Ufudu]

Thanks Roni,

I have done the mod, took about 30 mins and it works well. Lights now come on quite early on the pedal travel and at full brightness. [frame][/frame][frame][/frame]

[mike.perry]

The brake light switch is either on or off. There are two switches available, screw terminal or spade terminal

[Ufudu]

The brake light switch is either on or off. There are two switches available, screw terminal or spade terminal

No, unfortunately my switch shows a variable resistance, with the lights going from dim (light pedal) to bright (pushing quite hard as in emergency stop)

Now it's bright immediately from a light (PTP) pedal action.

[mike.perry]

Checked mine yesterday and they are either on or off

[bmcecosse]

Indeed - but at what pressure? The MOT won't catch this - because they just plant the boot and ask if the lights are on. The 'resistance' showing here will probably get worse and worse till it eventually doesn't trip the relay...... I would source another switch.....

[Ufudu]

Agreed, a new switch will be put in some time soon.

I can't recall that I saw this problem when first installed (Feb this year). As I said it was a new switch from a reputable supplier.

Can it deteriorate so quickly? I guess the contacts are oxidising due to sparking in the presence of contamination or not being sealed properly.

At least the relay draws only 100mA vs the few amps (5A?) of the stop lights so any arcing at the stop switch contacts will be minimised.

It's worth keeping an eye on...

[katy]

I can't recall that I saw this problem when first installed (Feb this year). As I said it was a new switch from a reputable supplier.

I'd suggest that you get after them for a replacement switch.

[alexmcguffie]

Fit a new switch and go back to standard. You've now got 2 sets of contacts that can fail instead of 1 as you should have originally.

[Ufudu]

OK will do.

Please can one of the the moderators delete this thread to prevent any litigation due to brake light failure in the event someone installs a relay.

Thanks

[tysonn]

Surely you're joking?

[irmscher]

Hey my minor caught fire doing this no win no fee

[Roni]

Fit a new switch and go back to standard. You've now got 2 sets of contacts that can fail instead of 1 as you should have originally.

If you can tell me where to find a guaranteed to work switch, maybe. With the relay it is a lot less likely that one of the sets of contacts could fail.
The relay inclusion into the wiring was sighted by a certified vehicle safety inspector who had no problem with it.

[alexmcguffie]

Roni,
Electrically, there is no problem using a relay as shown in the circuit diagram above. Obviously though, the more components you put in a system then the more chance of one of them failing. With the relay added, if either the pressure switch or relay fail then the lights stop working. If you want 'double redundancy' as used in safety critical systems, fit 2 x brake pressure switches and connect them electically in parallel. That way, if one fails then the other will still work. You would still need to check them electically from time to time to make sure neither has failed.

If you want a reliable pressure switch, find an original second hand opne on ebay.

[Roni]

If you can find one that has a seller willing to post outside the UK.

[alexmcguffie]

If you're prepared to pay the postage then I'm sure someone will. You better start contacting sellers

[dalebrignall]

i am running my 52 year old switch no probs , changed my girlfriends one twice in 3 years

[katy]

Ufudu, maybe you just got a defective switch.