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Old 05-24-2017, 04:34 PM   #1
MPETE
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Brake pressure switch function ?????

OK, 96 S10 4.3 5 spd. The brake pressure switch on the proportioning valve is a one wire switch. How does it work? Is it open all the time and then close to ground when there is a problem? Or the opposite, Closed to ground all the time and then open up when a problem pops up?
Reason is I have deleted ABS, and added a Wilwood adjustable proportioning valve. It has a 2 wire pressure switch on it and I am trying to figure out how to wire it into the factory system.
Should I cut the connector off the factory wire and connect it to the 2 wire switch and then the other wire to ground?
Thanks in advance.
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Old 05-24-2017, 08:12 PM   #2
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(Factory) Pressure differential switch is normally open, closes to ground with unequal pressure. (if one side looses pressure)
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Old 05-24-2017, 08:16 PM   #3
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According to Wilwood the switch on their valve is for brake lamps, not for warning lamp function. http://www.wilwood.com/PDF/DataSheets/ds715.pdf
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'91 Z70 Bravada lowered 4" 350 Vortec w/TBI, TCI-700r4, KYB's, 9C1 cop car steering gear, rear sway bar, yada yada...
'05 Subaru Legacy wagon (wife's daily)
'04 Subaru Forester XT EJ255 turbo, TBE, lowered 1.5" w/springs
'03 Subaru Outback
'92 K3500 4x4 dually dump, 454, 8' plow sander/spreader
'02 K2500HD single cab 6.0 4L80E

To help support this site with a donation click here
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Quote:
"The spirit of resistance to government
is so valuable on certain occasions,
that I wish it to be always kept alive.
It will often be exercised when wrong,
but better so than not to be exercised at all.
I like a little rebellion now and then." -Thomas Jefferson (1743-1826)
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Old 05-24-2017, 09:49 PM   #4
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Quote:
Originally Posted by mkgearhead View Post
According to Wilwood the switch on their valve is for brake lamps, not for warning lamp function. http://www.wilwood.com/PDF/DataSheets/ds715.pdf
well damn. I guess I should have looked into that a bit more. Didn't even think about it being for the brake lamps. The guy helping me, (ok he did the work, I just watched because I don't have the tubing bender or flaring tools) has the instructions that came with the prop valve, and I was just looking over things and trying to get an idea how this is going to work wiring wise. I'll look over the instructions tomorrow and see what it says.

second question. Since you say the switch is normally open, if it's unplugged, shouldn't the dash light be off then? And if it's on all the time, that means there is another problem somewhere, correct?
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Old 05-25-2017, 06:21 PM   #5
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Deleting the ABS could make it go on. Park brake switch can too.
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'91 Z70 Bravada lowered 4" 350 Vortec w/TBI, TCI-700r4, KYB's, 9C1 cop car steering gear, rear sway bar, yada yada...
'05 Subaru Legacy wagon (wife's daily)
'04 Subaru Forester XT EJ255 turbo, TBE, lowered 1.5" w/springs
'03 Subaru Outback
'92 K3500 4x4 dually dump, 454, 8' plow sander/spreader
'02 K2500HD single cab 6.0 4L80E

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My cardomain site
Quote:
"The spirit of resistance to government
is so valuable on certain occasions,
that I wish it to be always kept alive.
It will often be exercised when wrong,
but better so than not to be exercised at all.
I like a little rebellion now and then." -Thomas Jefferson (1743-1826)
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Old 05-29-2017, 05:25 PM   #6
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Quote:
Originally Posted by mkgearhead View Post
Deleting the ABS could make it go on. Park brake switch can too.
Mitch, can you confirm if a 96 S10 does or does not have a separate ABS light?
I don't ever remember seeing one. Don't have the truck or the owners manual close by to confirm myself.
I am going to look at the at the parking brake switch and see where that gets me.
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Old 05-29-2017, 07:02 PM   #7
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All with ABS have a red brake warning lamp and an amber ABS warning lamp. The VCM controls both lamps from inputs from switches and ABS unit. Red lamp can indicate park switch grounded (normally open), pressure switch grounded (normally open) or major (safety) failure of ABS. Amber ABS lamp can indicate wheel speed sensor, internal ABS relay etc..

I vaguely remember bad ground wires on the radiator support causing lights on too. Bad grounds do weird stuff. Electricity is like water, it wants to find a path back to negative and can flow backwards through lights and modules sometimes if it's normal path is gone.
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'91 Z70 Bravada lowered 4" 350 Vortec w/TBI, TCI-700r4, KYB's, 9C1 cop car steering gear, rear sway bar, yada yada...
'05 Subaru Legacy wagon (wife's daily)
'04 Subaru Forester XT EJ255 turbo, TBE, lowered 1.5" w/springs
'03 Subaru Outback
'92 K3500 4x4 dually dump, 454, 8' plow sander/spreader
'02 K2500HD single cab 6.0 4L80E

To help support this site with a donation click here
My cardomain site
Quote:
"The spirit of resistance to government
is so valuable on certain occasions,
that I wish it to be always kept alive.
It will often be exercised when wrong,
but better so than not to be exercised at all.
I like a little rebellion now and then." -Thomas Jefferson (1743-1826)
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Old 06-11-2017, 09:38 PM   #8
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Thanks Mitch. I haven't done much. In fact the truck is still sitting at work. I drive it to lunch about once a week, but have not looked into the brake lamp any further. ABS lamp is definitely burnt out because I haven't seen it function in YEARS, even at start up.

I have noticed when I start the truck and release the parking brake, the brake lamp will go out for split second then come right back on.
Not sure what to think about that.

The ground issue has me thinking. I have already moved the ground on the firewall once because of rust issues many years ago. I noticed during this process that the battery tray is in horrible shape and leads me to believe the core support is probably not in much better shape and since the ground wire is right in that area (brilliant idea GM) it probably has some issues that need addressed again. Not sure why I didn't think about that when I noticed how bad of shape the battery tray is in.
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