Brake Light Issues '64

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J

juiced99ws6

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Joined
Mar 8, 2016
Thunderbird Year
1964
So I drove my 1964 Thunderbird home about 400 miles and was under the impression from a friend that before I left on my trip home all my lights worked fine. First day I drove it to work after that I was informed my brake lights didn't work. When I got home I took a look and realized that they are just stuck on all the time.

If key is turned to the run position my brake lights come on and will not go off. I unplugged the pressure switch from the master cylinder and they stayed on. I then jumpered the wiring since I did on know if the switch was normally opened, or closed. Lights stayed on. If I turn on my signal the lights will blink between dim and bright like they should if brakes were applied and the turn signal was on.

If key is off and I turn the headlights on, all the lights work and the taillights are dim. as soon as I turn the key back on then the taillights light up bright again.

I really do not know where to go from here so any help is appreciated.
 
On the front of your master cylinder there is a switch. It operated by the brake hydraulics when you step on the brakes. It could be stuck on. Unplug it and see if your brake lights go out.
 
I have unplugged it and no change. I also jumoered the wires in case it needed to be closed to shut the lights off and no change.
 
Then there must be a relay in your trunk that is stuck on. I had a 64 for a while but it has been some time. I know 65 has a relay in the trunk behind the back seat.
 
That was my assumption as well. I could not find the relay, can you point me in the right direction?
 
Thank you so much, I had meant that i haven't been able to find it in the car though. I looked in the trunk at the forward part and can't see anything back there.
 
Thanks! That is where it was. I never did findthe exact problem but i ended up running new wires all together. I had replaced the relay and the switch with no change.
 
So what exactly did you do? I think I have it narrowed down to the stop light switch or the relay, but not sure how to check either one. Where did you run your wires?
 
Mine were stuck on. My relay plug had 2 hot wires as soon as ignition was turned on and 2 solid grounds at all times. After ensuring my brake light switch worked on the master cylinder I just clipped one of the grounds and spliced a longer wire and ran it to the brake light switch. I cut both wires off that switch and ran the new wire to it and another coming off to provide ground. Now the relay can only get a ground a ground when switch is activated. I don't know why mine wasn't working like that in the first place but now it functions fine.
 
Ok, but how did you check your brake light switch? I still dont understand how a fluid pressure can create an electrical current
 
The pole in the switch is throw by brake pressure rather than a push button or toggle switch. You check it using a multimeter and place a lead on each switch contact and have someone step on the brake to see if your resistance changes from OL to a resistance number. Normally about .1 ohms. If your lights are stuck on you can also just unplug the switch to see if they go out or stay on.
 
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