Brake warning light on (again)

Discussion in 'Mech Tech' started by Zebedee, Nov 27, 2011.

  1. About this time last year (before the forum crash anyway) i'd posted that the brake warning light on my westy had come on while i was driving and it was glowing dimly.
    I couldn't find anything wrong back then and it hadn't come on again when the engine was running until now.
    Started my van up today and got the light glowing brightly. :mad:

    Haynes says that if the light comes on then theres a leak somewhere, but i can't find one and the brake pedal is still nice and firm so it doesn't feel like one 1/2 of the circuit is duff. ???

    I found this diagram showing how it works but not what to do about it.

    Could it just be from the [glow=red,2,300]FACT[/glow] my van hasn't moved for 3 months and the brake fluid has absorbed a little water and caused the master cylinder to corrode and not return fully?

    Could it be corrosion on the brake light/warning light switch terminals on the master cylinder?

    Any suggestions?
    I cant' remember what was said last time. :-[
  2. it could just be a faulty switch
  3. I pulled both the connectors off the brake light switches and the light still stayed on.
    The terminals were still nice and clean and shiney so i can rule out a bad connection at the switch.
    Suppose it could be a duff switch.

    Not checked to see of the brake lights still come on as i can't be at the brake pedal and the back of the van and my missus wouldn't come and look because it was raining. ::)
  5. off topic, where did you get your steering wheel cover from?
  8. From what me and my dad can figure, with the plugs removed from the switches by putting a test meter across teminals 81 and 82a without the brake pedal pressed should show an open circuit and across teminals 81 and 81a a closed circuit.
    Pressing the brake pedal, if the swiches are ok, these readings should reverse ie 81 to 81a open circuit 81 to 82a closed circuit.
  10. Switches check out OK with a test meter attached. :(
    Wiring on the warning light is all correct too, though if the wiring light is faulty (maybe due to moisture getting in) i suppose it could make it stay on.
  13. i'd second removing the bulb ;D
  15. snotty, from the wiring diagram in the haynes it looks like there should be 12V at the 15 terminal (as it comes from the fusebox) and also 12V at the 61 one when the engine is running (as thats from the alternator) but not 12V when the engine is off. 31 is earth and K is from the switches on the master cylinder.
  17. jivedubbin

    jivedubbin Moderator

    i actually have a bulb and nothing else , no wiring just the bulb and holder . but it fills a hole in the dash and its green
  18. Heres a circuit diagram for the wiring for the warning light:

    From the look of it 12V is coming from the fusebox to the warning light all the time the ignition is on (engine on or off) but theres only 12V from the 61 terminal (alternator) when the engine is running and only 12V from the brake light switch when the pedal is pressed and theres a fault.

    From my (limited) understanding, if the engine is off, 12V passes from the fusebox, through the light to earth along the 61 terminal to the alternator so it lights up.
    When the engine is started and all is well with the brakes, 12V is coming from the alternator (putting out the alt. light) and 12V is coming from the fusebox so the light is off.
  19. I figure as the brakes still work fine that i must have disturbed the wiring to the warning light when i fitted my stereo a few months back. :-[

    Problem is getting the dash panel out to get to the back of the warning light is a swine now as i fitted a rev counter and the mounting bracket seems too big to fit through the hole, even though it went in fine. :mad:
  20. I'm impressed :). Your description is correct. With the engine off, but ignition on, the bulb will light up, presumably as a self test function. When the alt pulls the diode up, the light should go off.

    Sure you haven't got another wire going off to a handbrake switch?

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