[alfa] Re:74 GTV brake light ON

["Dean W. Cains" <dwc@xxxxxx>]

Hi Bob:

The pressure switch you asked about is on the right inner fender, under the 
Spica air filter, near the firewall.  You'll find it screwed into a cast 
steel junction of four brake lines.  The junction has two inputs: one from 
the front circuit of the master cylinder (which eventually goes to the RF 
caliper) and the other from the rear circuit of the MC (which later gets 
split between the two rear calipers).  Inside that junction is a floating 
piston, that will be forced one way or the other, if there is a big enough 
difference between the front and rear brake system pressures.  If the 
piston moves all the way to one side, it grounds the switch, and the brake 
warning light is activated.  If the light is activated with no brake pedal 
pressure, you've either got a bad switch, a grounded wire to that light, or 
a ground at one of the two other switches in the circuit (the one on the MC 
reservoir, or the handbrake).  If the switch is bad, it's unlikely you'll 
find a new replacement, but bear in mind that it was a feature that only 
existed for a few years anyway.  BTW, all three switches should be normally 
open.

Regards,

Dean
Lutz, FL
'74 & '87 Spider Veloce's


At 12:01 AM 10/24/2003, you wrote:

> Date: Thu, 23 Oct 2003 20:10:59 -0700
> From: "Bob Gauthier" <gauth@domain.elided>
> Subject: [alfa] 74 GTV brake light ON
>
> Hi Friends
>
> Today all of a sudden the brake idiot light on the dash turned on.  Pulling up
> on the parking brake handle increased the intensity of the idiot light, but
> not to say that the light was dim without the Park brake.
>
> Checked the fluid level, good.  Between the contacts on the cap of the brake
> reservoir, closed cicuit on both caps (which seems odd as I thought the float
> would drop, putting the brass hat across the terminals-- not sure how this
> thing works!)  Floats are working, they rise to top position with the cap
> off.
>
> Brakes seem ok -- I don;t detect any vacuum leakage or hydraulic leakage.
>
> Two questions (maybe three)
>
> 1.  Is the reservior cap switch gizmo supposed to be normally closed when
> filled with brake fluid?
> 2. Where is the so-called 'pressure switch' in the brake circuit located (its
> on the schematic but I don;t know where to locate it on the car!)
> 3. Any other ideas?
>
> Thanks,
>
> bob
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