Brake pressure warning switch

kylegordon · Oct 3, 2009

Afternoon all,

I'm in the final stages of replacing the wiring loom on my SWB 1981, and it's time to do the brake warning system. It's got the differential pressure warning switch between the two brake circuits, but I'm not sure what behaviour it should have.

Should the switch be closed circuit when there's a failure, or open circuit? At the moment the light comes on permanently, and the relay gets rather warm, leading me to think it's wired incorrectly, the switch is broken, or my brakes are needing bled/tweaked/fixed.

Finding out the behaviour of the switch will help me decide which system is incorrect. Any thoughts?

Cheers

Kyle

dr pepper · Oct 5, 2009

Mine is open so I assume closed indiactes a fault.
Dunno why the relay gets hot, even if its on all the time it shouldnt, anyways I wouldnt have thought a relay would even be in the circuit, the switch normally goes direct to the light.

Dazz · Oct 5, 2009

This any help

dr pepper · Oct 6, 2009

Looking at that then the contact will normally be open, and will ground if there is an excess of pressure differential between the front and rear lines when the pedal is pressed.

kylegordon · Oct 11, 2009

Hi folks,

Thanks for the wealth of info! Although my switches are in perfect order, it's kinda highlighted that my cabling loom for this purpose doesn't have the switch terminals in parallel like the schematic requires. Instead, my wiring loom seems to expect the switches to be in series, breaking the circuit open when there's a fault.

To save the confusion, I've cured it all by putting the whole loom in a box in a drawer int the garage. I'm not convinced it worked in the past 10 years anyway, and I won't miss it after this refurb

Cheers again all!

Kyle

dr pepper · Oct 13, 2009

If theres a light on the dash especially for this then you might want to remove it, some mot guys grumble if its not connected.

kylegordon · Oct 17, 2009

Yep, the light is gone as well. I don't like having lights, indicators and switches for things that aren't connected anyway

Kyle

Brake pressure warning switch

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