Brake light switch

[nelmo]

Has anyone ever tried using a reed switch as a brake light sensor?

https://uk.rs-online.com/web/p/reed-switches/9058910

I currently have the standard hydraulic-powered switch and it's not great; flickers too much and needs decent pressure to come on.

[IanS]

A reed switch requires a magnetic field to activate. The simplest switch is a mechanical one fittted to the brake pedle just like ford fitted to the sierra.

Though I can see that fiting a magnet to the brake pedle and mounting a reed switch near by could work but would require some adjusting.

Most reed switches connect when a magnetic field is applied so you might need a relay to change the switching action over.

[nelmo]

Sorry, yes, you need a magnet as well and I can see it being fiddly but with no mechanical involvement, it should be trouble-free for life.

I'm assuming I'd just connect wires from the reed switch to the same wires that currently run from my hydraulic switch? I assume that is also just a switch and it enables the circuit to light the brakes?

Parts are less than a tenner - might give it a go...

[IanS]

For this to work (using the same wires) the magnet must be away from the switch when the pedel is not pressed and must activate the switch for the full travel of the pedel.

[richyb66]

I used a motorbike rear brake switch. It's got a spring on it that's pulled by the brake pedal. Works far better that the microswitch I used before and it's easy to adjust should the need arise.

[toriitom]

A switch is not just a switch. 

Switches come in two varieties, Normally Open and Normally Closed, so you need to ascertain what type you have in your car before you run out and buy one of the wrong type.  I would assume that the brake light switch that is controlled by the brake fluid pressure would be a N.O. switch and it closes when the brake pressure activates it.

Reed switches activated by a magnet come in both varieties so be careful about which one you use.

I would be more inclined to use a micro-switch with the arm on it.  These have 3 contacts giving the benefit of having both N.O. and N.C. contacts so should suit most users needs.  Available from RS for under £5.

 

 

[nelmo]

47 minutes ago, toriitom said:

  Available from RS for under £5

£5! The reed switch is £1.50 and the magnet is 60p! OK, I did have to buy a bag of 5 switches... 

Thanks for the advice but I really like the idea of no moving parts. I'll give it a go first and I can try one of the other methods if it doesn't work out. 

[richyb66]

I previously used a microswitch with a roller on the end of the arm. It kept moving relative to the pedal and was hard to adjust. My brake lights were either always on, or not working at all.

I was glad when I finally sacked it off.

[IanS]

NC reed switches are even more sensitive to correct mounting than NO reeds in my experiance.

[Sparepart]

If you are using the usual 21 watt filament stop lights, the reed switch needs to comfortably handle 42 watts (2 bulbs) at 12 volts, i.e 3.5 amps. So you need a swich that is rated above 3.5 amps at a minimum, the more above this the better.

[nelmo]

11 hours ago, IanS said:

NC reed switches are even more sensitive to correct mounting than NO reeds in my experiance.

Yes, my concern was how much they are affected by vibration as our cars are not the smoothest  . I'm planning on fixing the location of the reed switch (with a bit of foam backing, maybe?) and then attach the magnet with Silkaflex-type stuff, which will give me time to move it around with the ignition on and pressing the brake pedal...something like that.

[nelmo]

9 minutes ago, Sparepart said:

If you are using the usual 21 watt filament stop lights, the reed switch needs to comfortably handle 42 watts (2 bulbs) at 12 volts, i.e 3.5 amps. So you need a swich that is rated above 3.5 amps at a minimum, the more above this the better.

I *think* the wires currently attached to my hydraulic switch go via a relay on the main fuse board (GBS standard loom), so hopefully not an issue?

And I've got LEDs....  

Edited September 30, 2022 by nelmo