Brake Effectiveness Light / Switch

[OzSpider]

Hi team,

Random question for the knowing. Mid restore and refreshing the brake system in my 1975 CS1 (USA model but now LH drive in Australia). The brake failure dash light is controlled by the brake switch and according to my Haynes Manual, the "brake effectiveness" switch which is on the pressure side of the master cylinder. Sorry its a pretty poor photo, but basically it looks like a normally closed pressure sensing switch which is in series with the brake light switch, such that if you press the brake and this pressure switch doesn't see pressure then the brake light on the dash lights up? I may be wrong.

Modern cars seem to just look at the brake fluid level in the non-pressure side of the master and if the fluids low the light comes on at any time.

My question is would you recommend removing (or avoiding buying a new one of these) and adding a fluid reservoir float switch or is the 50 year old Fiat technology a better way to detect bad brake hydraulics?

[18Fiatsandcounting]

You're close. This "junction box" senses the differential in pressure between the front hydraulics and the rear hydraulics. Electrically, all this junction box does is provide a ground connection for the brake warning light on the dash, exactly the same as the little button switch under the lever of the handbrake. So, if you lose pressure in either the front or the rear brakes for whatever reason, the warning light will light up when you press on the brake pedal.

The only downside to this device is that if you lose pressure in both front and rears, the light won't come on as it's sensing the difference in pressure and not the absolute pressure.

-Bryan