FireDemonSiC

Hey guys, never noticed this until tonight when I was checking my fluid level, but there is a single tan wire that goes to what looks like some sort of sensor in the top of proportioning valve. What function does this serve?

Apeiron

Pressure differential switch to light the brake warning lamp on the dash.

FireDemonSiC

Interesting. Does it utilize the same brake light that comes on when the parking brake is pulled or is this one different?

Apeiron

Same light. Pretty much every car on the road is that way.

FireDemonSiC

Under what circumstances would this trigger the light?

Apeiron

When pressure in the front circuit is substantially higher than the rear, or vice versa, such as you'd have with leaking or broken lines.

FireDemonSiC

Interesting. Learn something every day.

Is there a way to verify if it is functioning correctly? Can the wire be grounded?

Al Hasse

Yes, when working properly, the wire sends a ground to the brake warning light in the dash, completing the circuit. Ground it and the dash light should come on (with key on).

z 28 jari

iTrader: (1)

And if light is on(for example after bleeding brakes)you can reset that pd switch by pressing pedal real hard.

TreeFiddy

This has piqued my interest - my switch has never been connected due to the lack of a connector/pigtail - the good ol boys PO's must have made off with it years ago. Tan wire just hangs there, tucked up out of the way.

Not of huge importance, but anyone know where to get one or at least have a pic?

Al Hasse

Same style connector as on the head-mounted fan switch, knock sensor, etc.

From two different cars, the first is my 92 V6 with the prop valve still installed and in use, The second is on my 89, which has an adjustable prop valve to the rears, and an LS1 master cylinder with level switch that I use instead, thus the other wire coming out of the loom.

sofakingdom

iTrader: (1)

Every GM car had this same thing, for a couple of decades.

Just go to the junkyard and look at any of em from the late 70s up until the early 90s.

TreeFiddy

Not here in Oz apparently, always wondered what it looked like. I had a cursory look thru the local wreckers a few year ago, hoped maybe 80's Commodores would have used the same thing, but no. Thanks for the pics Al.

Apeiron

Even in Oz. Pretty much every GM car built since they decided dual redundant brake circuits were a good idea.

TreeFiddy

I'll have more than a perfunctory glance when I'm down there next, this is not something I've gotten highly motivated to fix

TreeFiddy

Fwiw - was at the local wreckers today - all 70's-80's-90's Commodores/ Holdens I could find used a master cylinder with what looks like an integrated proportioning valve, that has a 2-pin connector for the brake switch.

Sandslot

iTrader: (2)

Did you resolve your issue and have it working? It's important you know if you've lost one of the halves of your brake system. On our Camaros, the brakes have what's called a vertical split system - one circuit for the front brakes and one for the rears. Most FWD cars have a diagonal spilt system where one circuit is LF/RR and the other is RF/LR.

TreeFiddy

Same over here, all cars on the road will have a split system of some persuasion in case of failure - it's an ADR requirement.

Haven't found/invented a pigtail for the warning light yet. I have lost brakes 3 times in my driving life - trust me you're suddenly too busy with other things, to worry about if your dash light has come on

Al Hasse

That same style connector is used for the fan switch on the passenger side head, and for the knock sensor. Only difference should be the wire color, and a replacement will most likely have a white wire.

TreeFiddy

My engine wiring was butchered in an engine swap by a po - no knock or temp sensors on the block - and I've never seen one of these connectors used on any car for any purpose in the wreckers. Never come across an sbc for that matter. Afaik the sbc was not used in any car sold in this country.

Upshot is I've never come across one of these connectors in the flesh. It's not big deal, when I get around to it I'll just solder a wire onto the prop valve connector.

TTOP350

iTrader: (8)

Kinda close in idea but they are waay different. You can't swap them on each others sending unit/switches at all..

Al Hasse

I geuss they are different, though similar looking. They have differnt part numbers. I tried to find the brake connector part number for comparison, but no luck, thought it might be the same or similar to the cooling fan switch connector since all each of them does is route a ground - one to light a bulb and one to energize a relay.