Power to proportional valve? How?

[R8rPhan]

As I was removing the front harness in preparation for rewiring my 73 chevy C10 (frame is later year, but don't know what), there was a brown wire coming from the power brake proportioning valve (mounted on the frame near the radiator)..

Don't currently have power brakes, but the cab has the bolt pattern that says it came with them, and I also have the booster/master cylinder off of a donor 88 suburban that I plan to install to have power brakes on the truck..

So I want to make sure the valve has whatever electrical it needs...

Anyone, have any idea what I should supply power to this with? Is it full time 12v, or is it switched by something? If so, what? How much current does it draw?

 

[DanMcG]

Thats for the brake pressure warning light and should connect to the instrument cluster wiring harness. 73-76 is a 18 gauge tan wire.

 

[77 K20]

That wire doesn't get power: the signal it puts out IF something goes wrong is a ground.

Basically inside you can think of it as a teeter-totter. You lose pressure in either the front or the rear brakes and it will "tip" to one side and ground out. Then send a ground signal to your dash to turn on the warning brake light.

 

[R8rPhan]

Okay, great!

So, if my current cluster doesn't have a warning light, then I can add make one one later when I do the upgrade to power brakes... Just a light is all I would have to connect it to, right?

 

[77 K20]

Yeah- you could bring that signal ground wire to a light bulb and have the other side of the bulb/LED just wired to the battery.

I'd think you would already have a brake light even if you didn't have power brakes. Normally there are two ways to turn on the brake warning light. The proportioning (combination) brake valve and then a switch from the parking brake.

 

[Rusty Nail]

^yes.
Parking brake also.

 

[R8rPhan]

Yeah- you could bring that signal ground wire to a light bulb and have the other side of the bulb/LED just wired to the battery.

I'd think you would already have a brake light even if you didn't have power brakes. Normally there are two ways to turn on the brake warning light. The proportioning (combination) brake valve and then a switch from the parking brake.

On the new inst cluster I'm getting there is a warning light for the eBrake...

Hadn't thought about it, but what triggers that light? I don't remember detaching any wiring to any switch on the ebrake pedal.. Did they have such warning lights back then?

Sounds like I can use that light for the prop valve though...

I guess what you guys are alluding to, is a parallel circuit to the brake warning light.. one from the eBrake and one from the prop valve.. either one providing a ground that energizes the light...

Is that right?

 

[77 K20]

Maybe in '73 there isn't a parking brake warning switch on the pedal. If there is a plastic switch there then it would close and send a ground signal up to the warning light.

And yes, basically a parallel circuit (at least in newer trucks). One wire to the parking brake and one wire out to the prop valve.

And I honestly can't remember what years have what warning lights in the dash. I've owned a '77, '78,'79, '86, '87... and haven't used the parking brake really on any of them. They freeze in winter.

 

[Rusty Nail]

I was thinking thats the same light (bulb).

 

[75gmck25]

I've never found a wire or switch for a parking brake "on" light on my '75, and its a Silverado trim truck level that had quite a few options.

However, my truck does have the wire on the proportioning valve and a brake light (in the fuel gauge?) that will light up if the valve pops to either direction. I've seen the light come on for a short time when I'm bleeding brakes and the pressure is low in one brake line.

Bruce