On Fri, 17 Jun 2005, Comboverfish wrote:

> I guess I haven't run across this specific Ford brake switch but it
> sounds like it measures *brake fluid pressure*

Yep. The rest of the domestic auto industry figured out it was
unnecessarily problematic to detect brake application with a hydraulic
pressure switch...in 1961 or so.

> If this is true, why don't they use a momentary NO switch on the brake
> pedal (mechanically) like everyone else?

They do, they just *also* use this dumbassed always-live hydraulic switch.

> I'm not trying to sound smarter than Ford engineers

Er...why not? You've given every indication in every one of your posts
I've seen that you're considerably smarter than many of Ford's alleged
engineers.

> a low current, 5 volt threat to the brake fluid only with the key on
> verses a 12 volt 10-20 amp fused circuit hot at all times. What gives?

if the failure mechanism is as described (switch diaphragm ruptures, brake
fluid seeps into electrical chamber of switch, conducts electricity poorly
but enough to cause a high-resistance path to ground, which heats brake
fluid up to the burn point, fire ensues) then it's entirely possible that
the current rating of the 7.5A fuse is not exceeded at any time in the
process.

Remember, you can start a fire with nothing more than a Brillo pad and a
"dead" 9v smoke alarm battery.

DS