Brake light switch, Master vs pedal switch Options

[RKramden]

Unsuccessful finding prior posts on this, although I'm sure they're there.
Has anyone used a 2 prong pressure switch at the Brake master in lieu of the switch behind the Brake Pedal to control the brake lights? This is Utilized on a lot of cars and the idiot light for low pressure seems a bit overkill. I read Dave's post on Pelican and he noted the only time it ever lit up for him was when he over cooked his fluid racing and the light didn't come on until after his pedal hit the floor......Appreciate any thoughts
BTY this is a '74 non-stock with a 3.0

[Superhawk996]

You are completely misunderstanding what the differential pressure switch is for and how it works.

Not possible to use that switch to control the brake lights.

Edit: not trying to be snarky or abrupt. If you’re interested in how it actually works I’ll either lay it out or find a link for you where it was discussed fully.

[RKramden]

I guess I did not explain my question thoroughly.
I am installing all new wiring and was contemplating using a pressure switch to initiate the brake lights in lieu of the mechanical switch at the pedal. I understand the standard 914 single pole pressure switch at the MC is for monitoring brake fluid and ties to the light at the top of the gas gauge, and will not work for this application and I will need to install a two pole switch along with a relay etc.
My question was has anyone done this mod and were there there negitives with it.
Here is a link showing both machanical and hydraulic switches controlling brake lights

https://youtu.be/h6F9PauqvXc

[chmillman]

I have a ‘57 T-Bird that has a brake line pressure switch to actuate the brake lights as originally manufactured. Mine works fine (for now) but apparently they fail often enough that there are kits available to install a mechanical switch attached to the pedal.

One thing the mechanical switch can do is to allow you to tap the brake pedal and have the brake lights go on without enough pressure in the system to trip a pressure switch.

[bdstone914]

Porsche did that onwas used. With the single circuit master.. They often leaked. They switched to the mechanical switch on the pedal set when the dual circuit master cylinder wascused. I have rebuilt hundreds of pedal sets and rarely see a bad switch.
It works. Leave it alone. Nothing to gain. If it ain't broke don't fix it.

[brant]

start by saying that I don't know how those master switches work either.

but my guess is that when the master cylinder fails it pushes further than when the fluid is sealed in the system... then completes a circuit and sends a signal.

so if I'm right..
your brake lights would only come on when you were experiencing failure of the brakes... not useable for daily driving.

use the switch as designed

[RKramden]

Single pole pressure switch measures pressure imbalance and will complete the circuit to ground, thus lighting the warning light.
The dual pole uses hydraulic pressure to complete a circuit hence the two poles (in and out)
My Fiat Spider and my ‘64 bug both used a dual pole pressure to activate the brake lights

[Root_Werks]

Using a pressure switch for brake lights isn't a good idea. Converted my Bug from pressure to pedal moving years ago. Common conversion because pressure switches tend to require pressure before activating brake lights. Whereas a micro or movement switch can provide more warning to the inattentive driver behind you. As-in, brake lights come on before slowing occurs.