Brake switch 'normal function' and brake switch 'failure' are not the
same thing  They don't behave in the same way.

On 6/9/2014 8:18 AM, Steve Williams wrote:
> On 6/8/2014 5:13 PM, Mike B wrote:
>>    If one brake light switch fails and the other one still works, the
>> brake warning light will not come on.
>
> I studied the Bentley schematic for my model year carefully and
> concluded that it will, depending on the switch failure.
>
> The schematic shows the switches are SPDT, with their outputs wired so
> the brake warning light will come on if one switch stays at its NC
> (normally closed) position, presumably because it's not seeing
> hydraulic pressure, while the other switch goes to its NO (normally
> open) position.
>
> So if one switch failed so it stayed NC even with pressure, the brake
> warning light would come on.  If one switch failed so as to leave both
> outputs open, I agree there would be no warning light until the second
> switch failed.
>
>>    Jumpering one switch would not trigger the dash brake warning light.
>
> I think it might, but I'd have to study the schematic again.
>
>> The warning light on the dash is driven by the third terminal on the two
>> switches ... The third terminal goes to ground when the master cylinder
>> piston moves farther in the bore due to one or the other piston seal
>> failing ...
>
> I see nothing in the schematic about the brake light switches going to
> ground.  Each switches 12V between their two outputs.
>
> Hope I'm looking at the right schematic.
>
>>    It's really not hard to reach the master cylinder and brake light
>> switches, if you pull the entire instrument cluster, which is not very
>> hard to do.
>
> Thanks for the encouragement.
>
>>    Start at the fuse and check for voltage that goes into one side of
>> each switch, then out of the other side when you apply brake pressure.
>> If that all checks out ok, then the wire traveling back to the
>> tail-lights is open somewhere, possibly due to corrosion in a connector
>> at some point.
>
> That's what I was thinking.  The schematic shows another connector
> somewhere between the switches and the taillight assemblies.