1969 Brake Lights No Longer Working - Vintage Mustang Forums
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Old 06-17-2019, 08:53 PM Thread Starter
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1969 Brake Lights No Longer Working

I'm just about finished with a 1969 restoration. In the process, I gifted the car with a set of factory '69 power front disc vs the manual drum it started out with. As I put the car back together, I learned the brake switch did not operate the lights with the master cylinder and the power assembly I now had in the car. After some research, I learned there were different switches for manual vs power (as I recall) brakes, so I purchased a new brake switch to match what I had installed. After (a painful) installation, the brake lights worked fine. I went on to complete the car and have drove it maybe 100 miles as I've begun to wrap it up and I know the brake lights were working during most of that time. However, last night I happened to notice they no longer worked. After some diagnosis, I tracked power to the switch and I operated the switch manually by forcing it closed with a screwdriver--much like the master cylinder pushrod should do. When I did, the lights worked without issue. When I push the brake by hand while under the dash, I can see the rod doesn't move against the switch. Of course the engine is off and it would take one helluva push to move it.

What could happen that would cause this working switch and lights to quit functioning?

The car doesn't run a lot of vacuum at idle and I noticed the brake light problem while idling to a stop. I do know the brakes are hard to work at idle without a lot of boost. Could the lack of vacuum be contributing the inability activate the brake lights? Maybe I need to try it with the RPM up and decent amount of vacuum... If so, I might need to install some sort of vacuum storage canister similar what originally ran the heater controls.

And btw, I did see this thread ==> https://forums.vintage-mustang.com/v...t-working.html but my situation was a little different so I thought I'd write a new one.

1969 r-code Mach I w/ C6, AC
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Old 06-17-2019, 09:08 PM
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Didn't you prove with the screwdriver that it was a contact problem ? Low vacuum would be a booster issue. Brian
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Old 06-17-2019, 10:05 PM
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Iíve had issues with those switches too. I think that spring in them is too strong for the power brake cars. If you can find an OE switch, even used thatís a better bet.
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Old 06-17-2019, 10:19 PM
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I wish Ford would have kept the hydraulic brake light switch they used back in the 50's all the way up through the '64.5. It can be mounted anywhere in the brake system and you don't have to stand on your head under the dash to install/test/remove it. Why did something so simple have to be replaced with something so convoluted?
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Old 06-17-2019, 10:19 PM
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Originally Posted by kevin69 View Post
...After some research, I learned there were different switches for manual vs power (as I recall) brakes, so I purchased a new brake switch to match what I had installed. ...
NPD shows 2 switches for 69. One is for Manual Brake and one is for Power Brake.

https://www.npdlink.com/search/produ...0001&year=1969

Are you sure you got the proper one for the PB? make sure it's installed correctly as well.

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Old 06-17-2019, 10:28 PM Thread Starter
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Yup, my vacuum theory was easy to test and disprove. Back to the drawing board. What gets me is I know it worked for several dozen miles since I had others behind me who were looking for issues. Now itís 100% hard fail with nary a flicker. I really dont want to change out this switch again if I can help it. I have an epas in the car which makes getting to this thing almost impossible. Iím going to crawl under there again though Iím getting to old to do this with the drivers seat in!

I know this is crazy but I canít help but wonder if my ďmystery boltĒ has something to do with this. I found a large-ish bolt in the driverís footwell a few weeks ago and have been unable to find itís home. Itís the size of bolt that holds the dash to the interior pillar on either side (but they are all in place). Given that Iíve had this thing totally apart multiple times and for months at a time, I finally decided it was a bolt I left laying in somewhere under the dash when I put it all back together.

Time for a little deeper look...

1969 r-code Mach I w/ C6, AC
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Old 06-17-2019, 10:31 PM Thread Starter
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Originally Posted by 69GT350H View Post
NPD shows 2 switches for 69. One is for Manual Brake and one is for Power Brake.

https://www.npdlink.com/search/produ...0001&year=1969

Are you sure you got the proper one for the PB? make sure it's installed correctly as well.

Well, thatís what I found and I ordered the Power version and it was different than my old one (seems like the spring was a different color). I assume I have the right one and it worked for a few weeks.

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Old 06-17-2019, 10:33 PM Thread Starter
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Iíve had issues with those switches too. I think that spring in them is too strong for the power brake cars. If you can find an OE switch, even used thatís a better bet.
Iíll look but Iím guessing that will be a tall order. I do have my old manual switchósomewhere. Iíd steal the spring out of that but I think that is one of the differences.

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Old 06-17-2019, 10:39 PM Thread Starter
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Originally Posted by 69GT350H View Post
NPD shows 2 switches for 69. One is for Manual Brake and one is for Power Brake.

https://www.npdlink.com/search/produ...0001&year=1969

Are you sure you got the proper one for the PB? make sure it's installed correctly as well.

I might call westcoast classics—they have been my best oem source. I should also add that I’m pretty sure I installed it correctly. It took lots of futzing and that was when the drivers seat was out, the dash pad out and the dash fully disassembled. Nice picture of how the parts fit together btw. I can’t help but notice the master cylinder rod in the picture has a flat edge where the switch is mounted. I don’t recall mine having a flat side, just rounded-end rod (though its been nearly a year since I put this in).

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Last edited by kevin69; 06-17-2019 at 10:43 PM.
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Old 06-17-2019, 10:42 PM
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Iíll look but Iím guessing that will be a tall order. I do have my old manual switchósomewhere. Iíd steal the spring out of that but I think that is one of the differences.
I'm going to guess the PB spring is lighter than the MB spring. As the PB has the vacuum assist, the pedal requires less pressure to apply the brakes over the MB system. W/O the engine running, apply the brakes several times to use up the stored vacuum in the PB booster, and once the vacuum is gone, see if the switch activates when the pedal is depressed. If not, I suspect the switch has an issue, either an electrical connection/contact or the mechanical movement required to activate the contact. As you stated you can activate it manually with a screwdriver, I say there is an issue with the flat of the master pressing on the flat of the switch and traveling far enough to activate the switch.

Again, check the installation and make sure the parts allow the proper amount of movement to activate the switch. make sure the stud on the pedal does not have any excessive build-up that might limit the movement. Rust or excessive paint may take up needed space to activate the switch.

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Old 06-17-2019, 10:46 PM
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I might call westcoast classicsóthey have been my best oem source. I should also add that Iím pretty sure I installed it correctly. It took lots of futzing and that was when the drivers seat was out, the dash pad out and the dash fully disassembled. Nice picture of how the parts fit together btw. I canít help but notice the master cylinder rod in the picture has a flat edge where the switch is mounted. I donít recall mine having a flat side, just rounded-end rod (though its been nearly a year since I put this in).
Its interesting to look at the image, and try to visualize and understand that there has to be a bit of movement in the parts for the pin on the pedal and the round end of the master cylinder rod have to move a small amount to make the switch work. You might think with all those bushings that it was just a slight pivot when in fact there is a bit of "slop" movement as well.
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Old 06-18-2019, 12:00 AM Thread Starter
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Ok, firstómy master cylinder rod does have a flat as in the picture. I donít consider this a permanent fix but I was able to fix it temporarily by inserting a narrow strip of 22ga sheet metal between the master cylinder and spring plate. The tension holds it in place and it activated and de-activated 50 for 50 times. I guess this means as was stated earlier that I canít really trust this part. So this is ďfixedĒ until I can find a part I can trust...and find some small-framed young guy to stand on his head and change it out for me ;-)

Other opinions welcome!

1969 r-code Mach I w/ C6, AC
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Old 06-18-2019, 12:18 AM Thread Starter
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Its interesting to look at the image, and try to visualize and understand that there has to be a bit of movement in the parts for the pin on the pedal and the round end of the master cylinder rod have to move a small amount to make the switch work. You might think with all those bushings that it was just a slight pivot when in fact there is a bit of "slop" movement as well.
Yes, the same conclusion I came to. Everything here is fresh, so no buildup other than a coat (maybe two) of black paint. I wondered if that would be enough to prevent the slop necessary to work the switch. However, that doesnít jive with the fact that mine worked for a period as it was. I did learn that the switch will pivot a bit up and down against the flat of the rod. I found that when you pivot it up or down, it doesnít take much movement for that to set off the switch. So I guess, I could have installed it with a bit of an angle (instead of straight out from the flat edge) and if it managed to stay there for a bitóbecause it was newóit would work until it wore a bit and moved to its default position where there was not enough slop to trip the switch. Iíve temporarily fixed it by making it work with less slop due to the shim. Another approach may be to take it apart and try to ensure more slop with less or no paint on the pin<->master cylinder rod connection.

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Old 06-18-2019, 09:53 AM
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Sounds as though you have narrowed down the field and your pretty sure the problem is brake switch related ? I had a similar issue and the short story and solution was to get an authentic AUTOLITE C6OB-13480-A replacement. This is the switch in my power disc brake car now. I also have a back-up switch MOTORCRAFT C9ZZ-13480-B SW-864 in the event of a switch failure. When going through the same process you are involved with now I discovered the confusion over power vs manual switch's and the unreliability of the aftermarket replacements. Yes it is another of those PITA jobs. Removing the front seat is generally SOP, for me, when doing any work under the dash. While the work area is barely visible once you get your hand in there all visibility is gone. So a ' by feel ' assignment. Gotta wonder when during the assembly line process the switch was installed ? The direction of the plug tines, outboard, dictates the switch install position. I found the 2 nylon washers took up too much room on the shaft ? I made one of my own out of milk carton plastic. Anyhow the job is doable and with the proper switch should only have to be done once ? Brian
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File Type: jpg 69 pedal Assembly b.JPG (284.5 KB, 2 views)
File Type: jpg 69 Brake Switch C6OB-13480-A.JPG (193.8 KB, 2 views)
File Type: jpg 69 Brake Switch C6OB.JPG (197.8 KB, 2 views)
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Old 06-18-2019, 10:05 AM Thread Starter
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Yes it is another of those PITA jobs. Removing the front seat is generally SOP, for me, when doing any work under the dash. While the work area is barely visible once you get your hand in there all visibility is gone. So a ' by feel ' assignment.
Thanks for the comments. It's bad enough from the factory setup. I also have an electric power steering motor (EPAS) directly in the way, which significantly complicates access.

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