brake pressure sender

[10yearsgone 15]

Purchased stainless brake lines and a new distribution block/Proportioning valve.Brake lines wouldn't adapt to the block/valve and made my own (so I have a set of stainless lines for sale). Starting to do electrical work now and the sender is a one wire (a 2 wire sender won't fit in block). Ordered the pigtail kit, but still unclear from the wiring diagram, etc how this is going to work with the 2 wire configuration in the harness. Which wire do I connect to, both are even the same color? I'd think one would be live and another ground.

[rchappelear 28]

i think the two wire set up as long as one is power and the other ground it doesnt matter... it acts like an on off switch no matter which way it goes

[10yearsgone 15]

I'm only assuming one is hot and the other ground... I'd feel better about that assumption if the wires were different colors or if I could read the wiring diagram.

[Rsanter 152]

As far as I know the brake pressure sensor is a normally open switch. When pressure is applies it closes the switch so it will allow the electricity to pass.

Go from a power source that is always powered. Go to one terminal of the sensor. Go out of the other terminal to the brake lights

 

Why are you using one of those? Why are you not just using the switch that goes on the pedal?

 

Bob

[Midlife 814]

There's two brake sensor switches: one for the brake lights located at the brake pedal, and another for failure of the master cylinder.

[10yearsgone 15]

There's two brake sensor switches: one for the brake lights located at the brake pedal, and another for failure of the master cylinder.

 

That's what I thought this was. So is there an indicator on the instrument cluster? Any ideas on the wiring?  

[danno 128]

The factory brake pressure switch has the 2 wires on it. One goes to the ignition switch and gets connected to ground when the key is in the start position.  The other one goes to the light in the dash. If the one that goes to the light in the dash gets connected to ground, the light turns on.  The wire that goes to the ignition switch is there so when you try to start the car, the brake light should come on.  That way you know the bulb is ok.

 

If you have an ohmeter, you can verify this. The information I have is that the 2 wire connections on your factory switch are connected together in the switch. You should be able to connect both the purple wires together, and also connect them to your new switch. Maybe your pigtail will do exactly this. It is easy to verify, during the bleeding process. Start by verifying the light turns on when the key is in the start position, and open a bleed line to relieve pressure in the front brakes, and that should have the light go on also.

[10yearsgone 15]

Thank you danno.

[Midlife 814]

The factory brake pressure switch has the 2 wires on it. One goes to the ignition switch and gets connected to ground when the key is in the start position.  The other one goes to the light in the dash. If the one that goes to the light in the dash gets connected to ground, the light turns on.  The wire that goes to the ignition switch is there so when you try to start the car, the brake light should come on.  That way you know the bulb is ok.

 

If you have an ohmeter, you can verify this. The information I have is that the 2 wire connections on your factory switch are connected together in the switch. You should be able to connect both the purple wires together, and also connect them to your new switch. Maybe your pigtail will do exactly this. It is easy to verify, during the bleeding process. Start by verifying the light turns on when the key is in the start position, and open a bleed line to relieve pressure in the front brakes, and that should have the light go on also.

I'm not sure that tying the two purple wires together at the MC will work.  That will essentially take the MC brake switch out of the circuit.  What might be effective is routing the ignition power line to one side of the dash cluster light, then take the other side and route it to the MC brake switch where it would be grounded if the MC is bad.  That's a significant wiring change, though.

[Protowrxs 111]

I think danno has it. The two purples do tie together in the balance switch under the hood. The schematic runs from the bulb, out to under hood, and back to the ignition switch. If the safety switch moves either direction it grounds the wires or when the key is in start it grounds the wire lighting the bulb. Weird how they did it but that's how I see it at least. I removed the balance switch and used the wires to on a late model master cylinder low brake fluid sensor myself.

[10yearsgone 15]

I'll look over the wiring diagram again this weekend. Appreciate all the feedback. 

[danno 128]

I was thinking about it, trying to understand the reason why they would run 2 wires out to the switch, only to connect them together inside the switch. The reason has to be that if the connector to the brake switch comes off, the brake light will not turn on when the key is in the start position.  With a one wire system, this is the only thing you will not have. 

[Midlife 814]

By Gawd, Danno, you're right!  I looked at my schematics and the wires are tied together inside the MC line and are grounded whenever the shuttle goes left or right.  My humble apologies for thinking you were wrong.

[JayEstes 172]

I'm having problems with my switch (in the brake manifold under the hood) and I was really curious about this.  I can see down inside the connector and the 2 wires are connected.  I struggled trying to test it, and at first, I didn't understand the switch was mechanical.  Mine was stuck hard in the depressed (closed) position. 

 

As for testing it, the brake light was on all the time on the dash, so i knew something was wrong.  I finally realized that the "nub" that comes out of the switch must be a spring loaded shaft that is closed when pushed up into the plastic housing, and open when down into the manifold fully.  If the master cylinder fails (one of the chambers), the shaft in the manifold moves to one side (more pressure on one end from good chamber, and none on the other end from failed chamber).  When it is centered (both chambers good), the switch is "not depressed", because the shaft has a relief machined into it and the nub is not pushed up.  But if either cylinder fails, the shaft moves either fore or aft, and the nub gets pushed up into the closed position.

 

It looks like I need to buy a new switch for mine.  I finally pulled hard enough on the "nub" and it came unstuck from its depressed position, but no spring force left, and it doesn't appear that I can break into it to fix it.

 

Anyway, I'm hoping this is helping other people understand this odd little switch.  It took me some time to figure out what was going on, and the discussion above made it even clearer.  I appreciate the discussion from you guys above.  It's all making sense now.

 

Jay