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RareCJ8

E brake warning light

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looking to restore the factory ebrake warning light.  Recently did disc brake conversion in rear.  With 15 miles on it, hopped in to drive to work and forgot to release ebrake.  Smoked the new pads and tripped the proportioning valve.  Ugh.

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RareCJ8...Simple enough to restore, you've got the E-brake pedal switch.  Wiring through a fuse is straightforward.  Use key-on for the positive lead to prevent running the battery dead when the key is shut off and E-brake set!

Much cheaper to get the E-brake light working than to repeat the toasted pads.  Rotors okay?  They must have been glowing red...A testimonial to the 4.6L stroker motor, I'd say!

Moses

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 Some wiring diagrams show the E break circuit going through the proportioning valve. My valve has no electrical connections. I was able to source the switch from a jeep graveyard  and it was not cheap.basically a spring loaded plunger.  It seems the circuit is complete anytime the E brake lever is in the retracted position. Light goes off.  Once the lever is engaged the switch no longer makes contact with the lever and the light should come on.   i'm considering abandoning the factory speedo cluster location and add a bright LED right at level eyesight.  Time permitting must replace pads and rebleed system the brake pedal now is very mushy. Costly mistake for a very short drive.   Im still confused how to wire it up.  

 

image.jpeg

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RareCJ8...Without the proportioning valve lead, you have an easy wiring job.  I would feed a two prong (hot and ground) E-brake light with a constant "hot" or positive lead from the ignition source (to go off when key is off).  Fuse this lead.

I'd have the pedal switch complete the ground, like a traditional door jamb switch.  With the right pedal switch (a simple spring-loaded door jamb switch would work here), the ground at the pedal will be complete when the pedal depresses.  

This kind of switch grounds to its threads and the body/chassis.  You can make a simple bracket(s); position the switch and a plunger stop/arm to open/close the switch.  The switch closes when the plunger comes out.  When the pedal is depressed, the plunger comes outward under spring pressure.  This closes the circuit, and the light goes on.  When the pedal releases, the plunger closes and opens the ground circuit.  The light goes off...

Moses

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Getting close.  I think.  Below is pic of similar switch.  I grabbed this from web.  It screws to side of ebrake housing with spring loaded plunger.  With ebrake pedal retracted it makes contact with the plunger.  Engage ebrake and it no longer touches and a light will come on.  

image.jpeg

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RareCJ8...Have a feeling this is actually a ground switch like I described.  It has one lead.  That means when the pedal is depressed, the plunger comes out.  The switch closes and completes a ground between the wire and the switch mount on the bracket.  The bracket is a chassis ground.  The light would have a fused, key-on hot lead; this switch would be the ground.  

Note:  The 12V D.C. bulb or bulb socket requires two wires: one a ground, the other the hot lead.  Wired correctly, when the key is on, the hot lead is hot.  The E-brake pedal switch completes the ground...Simple.

If you cannot find this particular switch shown, make your own bracket and use a common ground-type door jamb switch (available at any motor supply, see a catalog).  Adjust the switch to do the same function as what you see here.

Use a volt-ohmeter to prove how this or a similar switch works...Check for a complete circuit to ground when the switch closes.

Moses

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Rarecj, this is a diagram of the E-brake switch on my 1994 Dakota. The switch is screwed into a bracket on the top of the pedal assembly, and has 3 wires to it. One is a ground, one is the power in from a switched source, and the third is a light output. It works on the same principle as a brake light switch, but, if you wire it so that it has a fused, switched source, then the third wire only gets power once the pedal is depressed, you can use any type LED, or even a regular dash light for the warning light. On the light side, hook one side to the wire coming out of the switch, and one to an available ground. This set up works very well, as i had gauge cluster issues with my truck for awhile, so i got a switch and harness from a local yard, and wired it up until i could fix the gauge cluster issues.

0900c15280089ca3.gif

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This is the OEM switch.  Cost $$ me a lot to be authentic.  The plunger is not isolated, as per the ohm meter. Tested all sections, its all one piece.    Mounts to ground and appears only connection is when pedal assembly makes contact with the top of plunger.  Not clear where is the 'switch' so to speak.  This should not be so difficult.  image.thumb.jpeg.4cc5c7e6ce0d92917ece8d3f882f1216.jpeg

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Looks like you could use the existing wires and instrument cluster brake lamp if you want...You also have the option of a standalone dash light for your E-brake, though that would require some new wiring.  

The upper diagram is essentially what I described.  However, the lamp hot lead is constant and not key switched; the ground is at the pedal switch with the ignition switch ground lead switched on and off with the key.  The ignition switched ground wire is the feed to the pedal ground wire.  Simply put, the ignition key opens and closes the ground lead, and the pedal switch also opens and closes the ground lead.

Looks like you have the pin tracing for using the factory wiring to the pedal switch.  The brake warning light hot lead is fused.

Moses

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Tnx moses but im still perplexed.  First, there are no existing wires for this project.  Id like to use the cluster light but all that is present is a very short threaded stud at the bulb, unknown if its even there or functional.  Short as in about 1/8" or less.  Since have to wire up from scratch, may locate a different light somewhere else.  Not a problem

The snag is how is this a switch?  What opens, closes the circuit?  This oem part is all electrically one piece.  Sure, there is the spring loaded plunger but that is not isolated From its housing.  In other words, once it is mounted to the ebrake assembly it is entirely grounded.  The pedal making contact with the plunger changes nothing.  Redundant.  Its hard to explain by typing.  Guess the question is what is the mechanism that activates the light?  I get that the ignition switch initially energizes the circuit but what action happens to allow light to come on?  

 

I might mock up a short example using a 9 volt battery some test leads and a low voltage led bulb i have.   and a pic tells a 1000 words.  

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RareCJ8...Use your ohmmeter, you're checking for continuity.  Hook one lead of your ohmmeter to the switch bracket.  Put the other lead of the ohmmeter on the wire terminal stud where the wire attaches.  Move the plunger in and out.  When the plunger moves in (opening the switch), the continuity stops.  When the plunger moves out until it seats, continuity takes place.  Since the switch attaches to a grounded metal pedal bracket, that continuity goes to ground.

The switch part that you cannot see (within the plunger sleeve) must have an insulating jacket, likely of nylon.  At the outer end of the sleeve is a steel/metal/brass/conductive seat.  That seat is part of the metal switch bracket.  

When the plunger moves in, the switch ground to the wire opens (no continuity), and the wire is no longer grounded.  When the plunger moves out (as the E-brake pedal depresses), all of the switch's metal parts should touch:  from the wire terminal stud through the plunger's stem to its seat, to the switch's metal base.  This completes the circuit to ground.  Confirm this continuity with the ohmmeter.

Envision what happens if you touch the wire lead directly to the pedal bracket:  It grounds out.  That completes the ground to the lamp.  Your pedal switch simply interrupts that grounding.  Like touching the wire to ground and removing the wire from ground.

Moses 

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RareCJ8...Use an inline fuse on the hot side to protect the ignition switch source.  Route the hot lead from an ignition switch "ON" source so that the light does not stay on after you shut off the key with the E-brake set. 

Position the switch so the switch plunger closes the switch at the desired point.

Moses

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will get to NAPA or ? soon to get a suitable LED light then wire it up.  inline fuse is easy--   stay tuned for updates.  i overkill all such connections with solder and shrink tube.

 

 

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Great, share photos of your handywork!  Others will benefit...Make sure the LED light uses two wires, you need a ground lead for your switch.  Some LEDs use the body or chassis for ground and only have a hot lead...

Moses

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Getting closer.  From what i can see when the lever is retracted (up)  it pushes the plunger in abd break the connection and light us off.  (Thus the soring is 99% of time under load.).     Engage lever (down) pressure off switch circuit closes and light comes on. I think i got it...

 

 

image.jpeg

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Yes, you've basically got it...Just remember that the closed switch completes the ground.  This should not be a hot (positive) lead at the switch's terminal.  This is the ground lead for your lamp.  When you install the switch on the grounded pedal assembly, you will create a short to ground if the wire is "hot".  The switch is designed to complete the ground.  

One side of your lamp will be a constant KEY-ON hot lead (fused for protection).  The other lead to the lamp goes to this ground switch at the pedal bracket.  

You have the switch on a non-conductive surface in this picture/test.  (Okay for testing the continuity of the switch with the plunger in different positions.) Once you install the switch on the pedal assembly, however, closing the switch (depressing the pedal extends the plunger like you show here) will complete the ground from the wire terminal to the pedal bracket—which is the same as a ground to the body/chassis.  The lamp now comes on because it has both the KEY-ON hot/positive lead and the ground/negative lead from the pedal switch.

When the pedal retracts, the plunger rises and the ground switch opens.  This breaks or opens the ground (negative) to the lamp.  The KEY-ON positive lead is still hot at the lamp, but the lamp has no ground.  With an open ground, the lamp cannot glow.  This is a 12V D.C. lamp that needs both a hot wire and a ground in order to glow.

Moses

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So the bottom of plunger goes to negative of light and switched fused hot to hot side of light.  Think i have it.  Was overthinking it.    Or i can just leave as is with a small battery and its all isolated from main system.  Found a perfect location for light near top of cab above sun visor.  No way to miss a red light there.

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Good, RareCJ8...If you have an easily accessible KEY-ON positive junction or wire, I would simply tap into it and put an inline fuse on a wire to the lamp's positive/hot side.  The other lamp wire would go to your pedal switch to complete the ground when the E-brake pedal depresses.

This way, you would have a system that works only when the ignition key is in the ON position.  You wouldn't run the battery dead by setting the E-brake, turning off the engine and walking away.  With the ignition key OFF, the E-brake lamp would not be working.  Turn on the key, you get an immediate red light if the E-brake pedal is on/depressed.  Retract/release the E-brake pedal, and the ground switch opens at the pedal—the red lamp goes off!  

Moses

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Re routed now switch is all ground side. Add inline fuse and we rock. Not pleased with the incandescent lamp so ordered a nice flush mount led. But I have concept down and found a switched hot lead too!  

Proof of concept.  

 

 

IMG_1054.JPG

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Well the old OEM switch design met its maker.  After about 30 activations of real time trail use the plunger post snapped off.  It was asking a lot for that small plunger make contact with the narrow rib on the brake lever.  Now to explore a more  robust switch design.  Back to scratch...  At least the circuit is in place.  Suggestions welcome.

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RareCJ8...Just a thought:  1955-59 Chevrolet and GMC truck mechanical brake pedal switches are spring loaded and have a lever.  This is called the brake light switch on these models.  The switch was once very popular and may still be available through light truck restoration sources, I found it readily at eBay...New, NOS or used.  

It's a robust switch that you might configure for your use.  Verify the on/off function, length of the lever throw needed and how to complete the circuit.  This is a two-pole switch, so in your case one pole would go to a solid ground, the other to your E-brake lamp to complete the ground when the switch closes.

Try to get your hands on a switch before buying to make sure it can serve your purpose...Test the lever throw and continuity.

Here's an image:

Image result for 1955-59 chevy brake light switch

If you use this approach, please share photos!

Moses

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