I have 2 cars–a '69 Cougar and a '68 Mustang, both with the same issue: the stop light swtiches are sticking on. I have been able to drive them for awhile after killing the battery in one because I didn’t realize it was sticking, and burning a couple of taillight bulbs in the other for the same reason. If I pull the brake pedal up with my toe, the switch goes off. And I’m talking, the pedal has only about 1/4" maximum play to pull it up to the top and to kill the switch/brake lights.
So I replaced the stop light switch in the Cougar just now, thinking it must be tired. But the new switch is exactly the same–it sticks unless I pull the pedal up 1/4". So I look in another car and note that the pedal can’t be pulled up–it returns to the top by itself like there is a spring somewhere, which there is not. The Cougar appears to have a fresh-ish master cylinder, and the Mustang’s master cylinder, I replaced myself about 3 years ago, with only a few thousand miles on the clock since. It seems to me that the “spring” that makes the pedal go all the way up and have no play must be from the rod of the master cylinder?
Do I need to replace the master cylinder to fix the pedal play/lack of return issue? The Mustang pedal was fine up until my recent drive to Canada, so I know that car is missing no parts and nothing happened to it.
Not sure about the '69, but on my '67 the switch fills a small gap between the pushrod and the pedal.
Push from either side and the effect is to close the switch. The force of the spring inside the switch keeps the 2 apart, and is usually rather strong.
Might try replacing the plastic bearing sleeve (I think they’re called) between the pedal and the frame. Maybe run a super fine grit sand paper over the contact surfaces where they contact. Could be giving more restriction to pedal movement? On my 67 it appears the pedal is returned by the master cylinder, since there is no return spring under the dash anywhere…
There is a different part number switch for manual brake applications. Your part store is likely selling you the wrong switch. You must also have the plastic bushing and plastic washer installed. Call WCCC and get the right stuff. Or click here:
Got the new switch from the local Mustang supply store–it’s the correct one. But I recall finding a part on the floor of my '68 under the pedal cluster–right before I left on the last trip, and it clicked in my brain. And the Cougar seems to be missing the two bushings. So I have a couple of parts cars, one with manual brakes. So I thought this was interesting–it came out of the parts car:
And this was what fell out of the California Special:
