Brakes Low Brake Fluid Sensor Connection 86gt With 93 Cobra Master Cylinder 5 Lug Conversion

[1200gt]

SOLVED - See solution at post #27

Hey guys I an 86 GT Vert. I,m trying to figure the best way to connect the Low Brake Fluid wires to the Cobra Master Cylinder setup.

I have not found a thread, on any site, that talks about connecting the low brake fluid sensor wires from the 4 eyed cars to the popular 93 Cobra, 87-93, and SN95 Brake Master Cylinders.

How can I make my low brake fluid senor in the dash work after doing the 5 lug conversion? I am using the 93 Cobra M/C. I can use the SN95 V6 unit but prefer the Cobra 1" bore.

It seems that some have 2 wires and other years have 3 wires....

I pulled a donor wiring harness connector for SN95 from the bone yard.... Not sure if it will work on the Cobra Reservoir....?

Thanks.

 

[General karthief]

You put the switch for the 86 into the prop valve in a bottom port?
I've read so much about this and no place I've found any discussion about the wires just the switch. Information overload!

 

[1200gt]

You put the switch for the 86 into the prop valve in a bottom port?
I've read so much about this and no place I've found any discussion about the wires just the switch. Information overload!

Thank for taking your time to help. I agree, i don't find anything about this subject, especially in the 5 lug conversion threads. However, I am getting the jest of how this process works. Last night, I too was in research overload! I did come across some info. I decided to go the research the engineers route. Meaning if they designed it, then info my be out there, and I did find some.

Once I get my head around it all I'm going to do quick Write-up about it for the next guy that comes along. I WAS surprised at the number of view on this thread that no one jumped in to comment. I'd assume there is a void of knowledge for the average Stangneter on this subject. I mean, how many 5 lug converts are there.....

Thanks again friend. Stay posted for the final solution.

BTW @karthief , you're right about just plugging the 86 wire connector onto the PV also properly named: COMBINATION VALVE. The warning light on the dash will then be operational for its intended purposes, however, on the 93 Cobra reservoir there will be no connection there...My challenge now is to see how I can improve upon the 86 warning circuitry utilizing the later model wiring...

 

[Mustang5L5]

What exactly are you doing, because one option would be to leave the 86 combo valve in place, and install a 1985 Lincoln town car MC which also has a 1" bore and would be identical in function as the 1993 cobra unit..albeit the older style MC.

I think the reason you don't see it often discussed is because most with that year tend to leave the unit in place and simply run the Town Car master cylinder and call it a day. Usually the only time people install other MC's (like the 94-95 cobra, or 94-96 V6 unit) is when the brake setup they run calls on a slightly different MC that the 1" bore wouldn't be ideal with.

The actual wiring is pretty straightforward. It's would simply be an open/close switch, and the only think you'd need to confirm is if it's normally open or closed with fluid in place. Then you could simply splice in the 1987-later connector and upgrade to the modern setup. You could even wire in parallel with the switch on the combo valve and the one on the reseviour....as it's wired in parallel with the switch on the parking brake. I think in this case, it needs to be normally open, and closing the connector in any of the 2 (or three) location will get the light to come on. I think the connector is compatible up to 2004 as the 2004 v6 also came with a smiliar 1" bore MC with same connections.

 

[1200gt]

What exactly are you doing, because one option would be to leave the 86 combo valve in place, and install a 1985 Lincoln town car MC which also has a 1" bore and would be identical in function as the 1993 cobra unit..albeit the older style MC.

I think the reason you don't see it often discussed is because most with that year tend to leave the unit in place and simply run the Town Car master cylinder and call it a day. Usually the only time people install other MC's (like the 94-95 cobra, or 94-96 V6 unit) is when the brake setup they run calls on a slightly different MC that the 1" bore wouldn't be ideal with.

The actual wiring is pretty straightforward. It's would simply be an open/close switch, and the only think you'd need to confirm is if it's normally open or closed with fluid in place. Then you could simply splice in the 1987-later connector and upgrade to the modern setup. You could even wire in parallel with the switch on the combo valve and the one on the reseviour....as it's wired in parallel with the switch on the parking brake. I think in this case, it needs to be normally open, and closing the connector in any of the 2 (or three) location will get the light to come on. I think the connector is compatible up to 2004 as the 2004 v6 also came with a smiliar 1" bore MC with same connections.

Hey thanks for the reply@Mustang5L5. As you can see from the previous post, I already have the 1993 Cobra M/C and Reservoir = 1" Bore. I'm also aware of all the possible option for the 5lug. When I pulled other parts from the Boneyard, I observed the wiring connections on the later model cars and in fact I cut two different wiring connectors off cars; both having different wiring. One even has 3 wires. Being short on any knowledge of the systems, and finding no threads that covered the subject, I decide to launch this thread.

Now since the launch of the thread others have come in to helped and I have gained a bit more knowledge of the mechanicals involved. I understand how many have been incorrectly calling the "Proportioning Valve' by name; when in fact it is a Combination Valve in function. That benig said, it made a world of difference in my understanding, and now, with my final plight to possibly integrate the later model early warning " Low Fluid Level" circuitry into the 86 somehow.

I understand now that to simply plug the OEM 86 connector into the PV is all that is needed to get the basic job done. Now I'm exploring other possibilities.

One poster above stated he never got a low pressure warning light from his 86 system when one of his lines when out. I'd like to think his PV/ Combo Valve was malfunctioning as being the reason why no alert. This brings me to think the later model stuff is better and might be worth doing if possible. Afterall, I'm still in re-build phase...

Hope this keeps me from looking too crazy...lol

 

[Mustang5L5]

Don't overthink it too much. The newer setups are simply a float switch that closes. 2 wires.

Not familiar with the 3 wire setups but that may be hydrovoost related.

 

[General karthief]

Lets see if I've wraped my head around this, keep in mind I do not have the brake up grade but knowledge is knowledge, some years, like the 86 in question, have a switch on the master cylinder, and some, the newer ones like the 04, have a float switch meaning something inside the reservoir, a float, triggers a switch, correct?

 

[Mustang5L5]

up til 1986, the fluid sensor, or pressure switch was on the combination valve (prop valve plus safety shuttle valve in one. Here's a good read in the first post on how it works
http://www.fordification.com/forum/viewtopic.php?t=77162

In 1987 and rolling over into some of the SN95 cars, the sensor change to a float sensor in the MC fluid reseviour. I know the 94-95 GT/V6 and 94-95 Cobra and 1993 cobra style switch are all compatible with the 87-93 setup

 

[1200gt]

Don't overthink it too much. The newer setups are simply a float switch that closes. 2 wires.

Not familiar with the 3 wire setups but that may be hydrovoost related.

Yeah, I'm not sweating it too much, but as @karthief described it: Knowledge is knowledge. This is where playing around with these stangs gets fun.... I'm going to look into the three wire set-up as well just to see how it works. Maybe it was a Hydroboost that I took the connecter from, but somehow I don't think it was. I been kinda keen on that system ever since I saw @raceoholic install his system; I would have been eyes opened for that.

I'm certainly going to read that link you provided above.

And, from what I have gathered on the 86 and earlier systems, and mind-you it was used by almost all car manufacturers, is the front and rear bowls on the M/C feed down into the combo valve (PV) and if either the fronts lines or the rears lines loose pressure or begin to slowly leak, that associated brake line path to the combo valve would have less pressure or become weaker and the PRESSURE DIFFERENTIAL VALVE (PDV) inside the combo valve will shift right or left towards the weakest pressure path. This shift in the PDV forces it to make contact with the internal PRESSURE DIFFERENTIAL SWITCH (PDS) contact point within combo valve. That contact is connected by wires going out to the dash instrument panel brake warning light and a chassis grounding point nearby. The warning light turns on because, yes as you said, it grounds out completing the PDS circuit. Very simple and effective... right.....

So why, after soooo many years of use, did Ford go away from this method and put the warning switch up into the brake reservoir? One thing for sure: At that change-over, it is no longer a "Pressure Differential Switch." It is then named the "Low Brake Fluid Switch." This is what I'm researching next. And if it happens to be a better system, which I believe it to be, and I can incorporate it into my car while I have everything apart, then I'll give it a go. I have a guess that it IS a much earlier, and more definitive indicator that the stuff that creates the hydraulic pressure (brake fluid) is slow; this indicator being triggered well before a system-wide failure ....

Thanks again for your input and the pics. BTW, if I find out more about the 3 wire setup I'll let you now.

Dwayne

 

[1200gt]

I was just thinking

This is what I'm going to do: I'll connect directly into the Pressure Differential Switch (neg. and pos. wires) with the same polarity wires of the "Low Brake Fluid Level Warning" circuitry wires. or just wire it in parallel to the 86 circuit. @Mustang5L5 suggested this solution up in post #4 and I had another stanger suggest this also. I think this might be a way to enjoy both worlds.... I just want to be perfectly sure about the wire polarity before I commit. Talk me down if you can....

 

[Mustang5L5]

I'll need to check the wiring diagrams on my 88 later to see how exactly the newer style switch is wired.

 

[1200gt]

I'll need to check the wiring diagrams on my 88 later to see how exactly the newer style switch is wired.

Great, I'm curious to see what you report.

I'll have to elaborate more on this later because I have to run out. I was planning to connect with you anyway later..... I assume the other 2 wire are the normal ground loop circuitry. I got a little more reading to do and I will eventually post what I find.... Thanks, have a great day @Mustang5L5.

 

[Mustang5L5]

Brake pad wear sensor? never seem such a thing on the fox unless the fluid sensor is being loosely referred to as a pad wear sensor.

Either way, here's the wiring diagram.

So I looked at my car. 3 wires. 1 black, and two the same with white tracer.

I didnt pull the plug to see if I had three contacts though

 

[Mustang5L5]

Here's a better shot of the wiring diagram. I actually think it's wrong. Given what I posted above on the old pressure switch setup above, the 88 wiring diagram calls it a dual brake warning switch and the description really doesn't seem correct for a float sensor

 

[1200gt]

Here's a better shot of the wiring diagram. I actually think it's wrong. Given what I posted above on the old pressure switch setup above, the 88 wiring diagram calls it a dual brake warning switch and the description really doesn't seem correct for a float sensor

Wow! The Plot Thickens!!!! at least for me... lol Hey, I'm not going to do any more babbling less I start dispensing erroneous information.... Now that I see that your car has 3 wires and I know none of them connect to any sort of Low Brake-Pad Warning Sensor for your Fox, I'm just going to refrain until I get facts. Your photos are getting me a bit closer to having real-world examples of the various systems.

Remember, I'm not digging at this just for the knowledge, I still hope to wire the 86 with the bowl switch incorporated.... why, because I want to do it... for those who might ask.

Look at the photos of the stuff I pulled from the boneyard. I pulled 2 diff. types of switches from different year cars; I wish I had paid more attention to the years of the cars

Anyway, one of the setups below looks like yours @Mustang5L5. The wiring colors seem to be a little diff. but they appear to follow the same purpose. The one all BLACK SWITCH setup looks like it comes from a car north of 1996 years. I am pretty sure not from a hydroboost car. The curious thing about it is the connectors have 3 contacts, however there are only 2 wires coming out on the chassis side connector....

Another important thing to note is that these reservoirs don't have wires directly on it at all; just the slide devise that slips through the reservoir opening and clips-on there. My theory at this point, on how the system works is that it is somehow MAGNETICALLY actuated... IDK. Maybe if the float drops close enough to the bowl, a stronger magnetic wave form is produced???? this is just babbling though don't quote me on it...

I'll keep digging into it

Below is the Reservoir that is being sold for the 1993 Cobra M/C. It come complete with the gray bowl-side contact connector already snapped in place. Notice it also has 3 contacts that mate to the chassis connector. This is probably going to be more like @Mustang5L5's 1988 setup. Not 100% sure on this though.. My new question for this is: Why 3 wire for this connection - there's no pad-ware sensors on these cars????

 

[General karthief]

Is there a way to test these setups? Maybe a using a nine volt battery and a light hooked to ground and filling the mc with fluid?
I have access to alldata during business hours if that will help.

 

[1200gt]

Is there a way to test these setups? Maybe a using a nine volt battery and a light hooked to ground and filling the mc with fluid?
I have access to alldata during business hours if that will help.

Hey guy! I'm sure there is a way to test this, and I plan to do it. soon. The circuits are not complicated at all. The stuff you really want to know in advance is circuit pathways, and how the different models routed the wires using different addition to the circuits like pad-wear sensors that turn on the warning lights - albeit from what I found the pad-wear sensor has a dedicated dash light...

Anyway, I was just coming on to post the info below that I just found on another site when I came across you reply. So, I'll post it now. Chat with you soon @karthief

Dwayne

This is info I got from a guy on another site. It seems to be TOUCHDOWN! for my team efforts... Now, just for knowledge, I'll dig into exactly what the 3 wire setups are intended to do on each car year group....

A fellow Stanger Wrote:

****Because you gutted your proportioning valve for the 5 bolt and rear disc upgrade you no longer have use of the switch on top of the proportioning valve****

I HAD TO EDIT THIS BECAUSE I THINK THERE'S SOME HOLES IN MY FRIEND UNDERSTANDING OF THIS SYSTEM.... MY UNDERSTANDING IS THAT THE GUTTING ONLY EFFECTS THE REAR LEG ON THE PV/COMBO VALVE, SO THEN NORMAL LINE PRESSURE SENSING SHOULD STILL BE ACTIVE FROM THE FRONT OF THE COMBO VALVE FUNCTION.... HOWEVER, IT'S STILL TOUCHDOWN! FOR CONNECTING THE LATER MODEL PLASTIC BOWL "LOW FLUID LEVEL SWITCH" TO THE 86! RIGHT...LOL

The part that would trip the light in the event of a line rupture no longer functions. The low fluid sensor in the new style master cylinder is meant to replace the old proportioning switch. The reservoir on the SN95 is not split like the older 86 master, when the fluid is low because of a rupture the fluid level inside the plastic reservoir is lowered and the light comes on to warn you of a brake issue. To facilitate a warning light on my conversion I used a pigtail from Ford, part number 3U2Z-14S411-NUB to plug into the low fluid sensor on my SN95 master cylinder, this pigtail has three wires instead of the two used on the original switch, find the two wires out of the three that would complete the circuit when the float inside the reservoir is at it's lowest point, cut and connect those two wires to the two wires that were attached to the old proportioning valve switch. You will now have a working light on your dash in the event you lose fluid. You can test it by pushing the float down and it will trip the red light that is also your e/brake light.

 

[General karthief]

Now that makes sense, I think.
Yes it does,

 

[1200gt]

I found a photo of PV cut-a-way. (THIS IS NOT an 86GT PV)

This is an 1986 Mustang GT Brake Pressure Control Valve: The Brake Switch gets tripped when internal Control Valve shift under a low pressure line fault thus illuminating the dash light by completing the ground circuit loop. The gutting of this valve is to take out the components on the right of this photo, still leaving the line side intact and functional... Right? BTW, these appear to be rebuild-able..

 

[Mustang5L5]

The switch is working on the shuttle valve portion of the combo valve.

When you guy the prop valve portion, you aren't touching this part. So it still remains functional.

I wouldn't put too much trust in it though as a few combo valves I've played with had the shuttle locked in place. 30 years or so, plus brake fluid overdue for a flush can corrode some stuff away.

The newer MCs also have a shuttle feature that acts to restrict flow to an open line. Unsure if the older MCs do this as well but want to say yes.

ford got rid of it when they went to the 3 port setup. Rather than read a shuttle position, they go on fluid level. Either will work, so don't overthink it.


Give me some time to get in garage. Watching kiddos at the moment so might be a delay. I think the 3-wire setup is black wire to ground, 1 wire gets 12v and when the sensor float drops, the sensor works off magnetic inductance, closes, and sends signal to other wire.

Both my wires are same color with same tracer. They look black but FSM says should be pink. Either way they look the same. I'll see if I can dig up 1993 wiring diagrams and see if ford updated the low fluid wiring as I think that is wrong. I've found a couple errors in it, but Obviously a few decades late for ford to correct it