aka Keith
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| posted on 27/4/09 at 08:37 AM |
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handbrake switches - How?
Can I ask a somewhat stupid question, but how do handbrake switches work.
The handbrake light on my car has suddenly stated staying on all the time (even if the handbrake is off - I have checked).
so last night, I took the centre panel of to have alook, and beyhold there is the switch. It can only see wire going in/or out of the switch into the
loom. So could someone tell me how they normally operate so that I can rule everything else out before ripping into the loom to replace the whole
wire.
Cheers
Craig
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jabbahutt
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| posted on 27/4/09 at 08:44 AM |
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I'm going to have a stab at this, but electrics aren't my strong point.
I believe you'll have one loom wire going to the switch which will be 12v. There should then be a short fly lead to earth.
When you pull on the handbrake the switch makes allowing the circuit to earth and the bulb lights up.
So with the h/brake off you should get 12v on a multmeter between the wire going into the switch from your loom and earth. The fact it's on all
the time indicates to me that the switch is continually closed.
Please check though as I'm a complete electrical fool. someone will be along in a minute to tell you the complete opposite
Good luck
[Edited on 27/4/09 by jabbahutt]
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daviep
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| posted on 27/4/09 at 08:44 AM |
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They switch to earth, if your lamp is staying on chances are the switch is stuck.
Take the wire off the switch, if the light goes out then the switch is faulty, if the light stays in you have a wiring fault and the wire is shorting
to earth somewhere.
Just thought does the same light do your fluid level warning?
Cheers
DAvie
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nitram38
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| posted on 27/4/09 at 08:45 AM |
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They normally have one wire from your brake resevoir and connect the circuit to earth.
The positive ignition feed goes to the warning light, the otherside of the light loops from brake resevoir switch to the handbrake switch, so that
either the resevoir switch or handbrake switch connects to earth.
Are you sure your brake fluid is topped up?
It could be warning you of a leak or that your brake pads are worn out
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Davey D
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| posted on 27/4/09 at 08:46 AM |
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they are normally a push to break switch - they cut the curcuit when the button is pressed by the handbrake.
all it does is earth the circuit through the handbrake. you can check by removing the wire from the switch, and touching it on your chassis
somewhere.. the light should then go off 
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nitram38
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| posted on 27/4/09 at 08:49 AM |
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quote:
Originally posted by Davey D
they are normally a push to break switch - they cut the curcuit when the button is pressed by the handbrake.
all it does is earth the circuit through the handbrake. you can check by removing the wire from the switch, and touching it on your chassis
somewhere.. the light should then go off
The light should go off when you disconnect it, not when you touch it to earth...........it will come on when touched to earth!
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aka Keith
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| posted on 27/4/09 at 08:57 AM |
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thanks folks, I will check the brake fluid, but have not seen any leaks under the car.
Last night, when I had the tunnel cover off, I tried the swith with my finger - moving the switch up and down - it made no difference to the ligh on
the dash.
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Richard Quinn
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| posted on 27/4/09 at 09:01 AM |
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quote:
Originally posted by aka Keith
thanks folks, I will check the brake fluid, but have not seen any leaks under the car.
Last night, when I had the tunnel cover off, I tried the swith with my finger - moving the switch up and down - it made no difference to the ligh on
the dash.
If your fluid level's low then moving the handbrake switch wouldn't make it go off. As most of us are least comfortable
with wiring etc, we tend to assume that any unusual warning lights etc are due to our wiring whereas they could actually just be doing what they are
intended to do.
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nitram38
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| posted on 27/4/09 at 09:01 AM |
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Your fluid could be low because of brake pad wear, not necessarily a leak.
Check your level first. Also make sure your resevoir level float switch isn't stuck.
[Edited on 27/4/2009 by nitram38]
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iank
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| posted on 27/4/09 at 09:12 AM |
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This is exactly why I don't like the brake fluid level warning light having the bulb test requirement done by a handbrake switch.
It makes people assume it's a handbrake left on warning rather than a real emergency, stop the car as soon as possible assuming the brakes are
going to fail really soon situation.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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nitram38
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| posted on 27/4/09 at 09:17 AM |
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Unlike a tintop which is a mystery to most people, I built my car so diagnosing a brake warning light is straight forward.
I think warning lights through the handbrake are a good thing because there is an alert to a problem.
Relying on remembering to press a seperate switch is a bit hit and miss.
I'd rather getting a brake warning and check it out, than find out when my brakes quit! 
[Edited on 27/4/2009 by nitram38]
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Steve Hignett
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| posted on 27/4/09 at 09:38 AM |
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Description
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iank
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| posted on 27/4/09 at 09:38 AM |
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quote:
Originally posted by nitram38
Unlike a tintop which is a mystery to most people, I built my car so diagnosing a brake warning light is straight forward.
I think warning lights through the handbrake are a good thing because there is an alert to a problem.
Relying on remembering to press a seperate switch is a bit hit and miss.
I'd rather getting a brake warning and check it out, than find out when my brakes quit!
[Edited on 27/4/2009 by nitram38]
It doesn't have to be on a separate switch which I agree is equally pointless. Mine is on a timer and comes on to test the bulb for 2 seconds
when the ignition is switched on. Having a bulb test function is really important on all safety critical warnings agreed.
If tin-top people need a handbrake now cooking the rear brakes warning it should be on a separate light IMO.
To me, and I've done a bit of industrial UI design in my time, combining warnings of unequal importance is just bad design, because humans tend
to assume the most common case is the only one. For example if they were stupid enough to combine the oil pressure light with engine service light -
people would just start to ignore it as 'it just needs a service' until they ground to a halt and find their engine is seized. Sharing
the function is just a cost saving measure not because it's a good idea from a design point of view.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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aka Keith
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| posted on 28/4/09 at 07:38 AM |
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thanks everyone. I got home late last night and headed straight to the garage.
popped the lid of the brake fluid resevoir, and it was a little low, topped it up, took out the float switch and gave it a good clean/recondition and
stuck it back in.
Light stays off now, but flickers when I use the handbrake, so I expect that the handbrake switch is a little loose. thats tonights job.
cheers
craig
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aka Keith
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| posted on 29/4/09 at 07:46 AM |
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Weel, got home last night and stirpped the tunnel. It loks like the handbrake light is a little temremental.
With brake fluid checked, and float swith cleaned, the handbrake light seams to be at fault. moving it with my finger sometiome sht light would go
off, adn sometimes it would flicker. looks like the connections are a bit iffy.
Do I have to fit a whole new handbrake? or can you replace the switch only. It looks like the switch is intergral to the handbrake , but I defer to
the knowledge of the fourm?
Cheers
Craig
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Gazeddy
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| posted on 29/4/09 at 07:48 PM |
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what handbrake lever are you using?
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aka Keith
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| posted on 29/4/09 at 08:29 PM |
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Gazedy, I do not know. It was on the car when I bought it.
I could try and contact the orginal builder to see if they can remember, but alternatively, any ways of identifying what it is from?
Picture is in my Photo Archive.
Cheers
Craig
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Gazeddy
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| posted on 29/4/09 at 08:34 PM |
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any pics without the trim on it? the switch on older ones should be replaceable. newer stuff will probly be moulded in. and need a new lever. im sure
just putting a push to make switch on it with a little bracke one wire from loom the other to ground
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aka Keith
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| posted on 30/4/09 at 07:46 AM |
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I have just looked at the orginal builders blog. It is a Metro handbrake, if that makes any difference.
Cheers
Craig
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