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aslanefe

Brake warning switch trivia

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Wasted some time today and learned something. May be it will help someone later on. 69, non-tach dash, converted to early 4 piston disc with a kit using original spindles. The brake warning switch that came with the kit is one wire, original switch on original drum/drum manual distribution block was 2 wire switch. Did not hook up the switch because I was going to figure out which one of the original wires I had to hook up to the new switch and turned the key to start and the brake warning light did not come on. During start the ignition sends a proof out to brake warning light and lights it up (light goes out when the car starts if no brake fluid leak on one of the lines to wheels). I had added a wire to pin 6 of instrument cluster and ran it towards the parking brake as I was planning to make a parking brake switch (using 3D print and berillium copper) and have my brake warning light come on when the parking brake is engaged. Grounded that wire as if parking brake is engaged and the light came on. Chased the proof out wire from the ignition switch (purple wire) to find out where it connects to the purple wire that goes to pin 6. Could not find the joint. The wire goes all the way to firewall connector, then to brake warning switch. The other wire from the switch goes to pin 6. I had checked continuity of the switch a few weeks ago and the switch was closed. As my brake fluids had leaked I thought the switch froze on closed position. When a switch has 2 wires going to it, usually it is a normally open or normally closed switch. The proof out wire had to be connected to pin 6 somewhere and I had followed the wire except about a foot of the harness. Then I realized that the pins of the brake warning switch must be connected inside the switch and it is not a normally open switch; it just contacts to the valve in the distribution block when there is fluid leak and valve moves to one side which grounds the wires sending ground to warning light to light it up.

In short, the brake warning switch on a 69 with non-tach dash (don't know others) is not a normally open switch; if you measure between the terminals and see that it is closed, it does not mean it is bad switch. Now I have to wrap the parts of the harness and put everything back together.

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The dual brake warning switch is serving 2 functions. One is to join the two wires internally  coming to it.  The other is the  momentary switch to ground  when a pressure differential is present between the front and rear brake hydraulics. You can splice the two wires together and T another wire to either pin on the two pin switch or use a single pin switch.  The prove out light bulb check for the brake light on the dash is performed by the ignition switch by providing power and ground in the  start position for the warning light test. The bulb prove out check does not test brake system just bulb operation.  

"I was planning to make a parking brake switch (using 3D print and berillium copper)"

aslanefe  if still you plan on making a switch I'd be interested in one!

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1 hour ago, gordonr said:

The dual brake warning switch is serving 2 functions. One is to join the two wires internally  coming to it.  The other is the  momentary switch to ground  when a pressure differential is present between the front and rear brake hydraulics. You can splice the two wires together and T another wire to either pin on the two pin switch or use a single pin switch.  The prove out light bulb check for the brake light on the dash is performed by the ignition switch by providing power and ground in the  start position for the warning light test. The bulb prove out check does not test brake system just bulb operation.  

"I was planning to make a parking brake switch (using 3D print and berillium copper)"

aslanefe  if still you plan on making a switch I'd be interested in one!

Yes I learned the hard way that the switch sends ground when there is pressure differential (which I thought was the only function of it) AND also joins the two wires to send proof out to pin 6. Now I know how to wire the new switch; keep the old switch attached to the harness, attach the wire from the one wire switch to the pin on the end of the old switch and you are done; no cutting of the original connector needed.

Yes making a copy of the original 69-70 style switch is on my to do list. I had succesfully made the metal part to fix a broken contact on original switch for my 70 Grande about 25 years ago which still works. I have to make the plastic part that fits to the original mounting holes on the brake pedal assembly to create a switch from scratch. I have a broken switch on my 70 Cougar to use for creating the 3D model; all I need is to find a few hours to create the part, get beryllium copper with right thickness,  make the contact part, heat treat, assemble, and test it. I will post it when I make one. Making a properly functioning turn signal cancelling cam replacement is also on my  to do list; I know, I have a long to do list. On a side note, I also learned that you do not have to tap into pin 6 behind the cluster like I did to get the brake warning light to come on when parking brake is engaged, you can tap into the purple wire going to pin 6 at the firewall connection. 

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I used a alarm hood pin switch.  Drilled a hole on the emergency brake bracket.  Tapped into the wire going to the pressure differential sw.  The foot pedal hits the plunger on the sw breaking the ground and turning off the brake warning light when the emergency brake is off.

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On 2/9/2019 at 3:50 PM, larryc94 said:

I used a alarm hood pin switch.  Drilled a hole on the emergency brake bracket.  Tapped into the wire going to the pressure differential sw.  The foot pedal hits the plunger on the sw breaking the ground and turning off the brake warning light when the emergency brake is off.

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I like this option. Simple and effective. There is nothing more frustrating than remembering you left the e brake on as you are pulling away. This should help prevent that.

 

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Yes that is an other option. Or you can use the 71-73 switch, both requires you to remove the pedal assy and drill holes at the right spot for the switch. The pedal assy already has the holes for the 69-70 switch and I have a few 69-70 cars with a broken switch or without switch. 

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For those running a non-stock brake system, my 2 cents worth...

I installed a jumper and disabled the switch.  Not recommending that for everyone, as it is supposed to be a "safety" feature.  Reason is that many of the aftermarket or late model master cylinders and proportioning valve setups don't have the switch.  I am using a late model stock Ford Ranger/Explorer master cylinder with Wilwood proportioning valve, and 2004 Mustang Cobra front and rear disc brakes.   The Cobra rear brakes have an integral parking brake feature which uses the hydraulics.  The car will not move with the parking brake installed.

 

 

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