Brake light problem
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New User
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Brake light problem
Anyone have any ideas on why my left brake light won't work on my 1966 F-100? It has the two filament bulbs one for the taillight and one for the turn signal/brake light. When the turn signal is activated the bulb filament illuminates but using the brakes won't make it work. All four turn signals work. Changing the bulbs didn't fix it. I checked the wires and they are all intact from the taillight to the cab. The fuse panel light fuse is also good. The right side works fine so I know the brake pedal switch works. I also tried replacing the turn signal flasher unit with a new 552 but the brake light still doesn't work.
Thank you.
Thank you.
Elder User
Joined: Aug 2004
Posts: 602
Likes: 1
From: Sacramento, CA.
If you don't have a voltage meter, Switch the two T/L assemblies and see if the right works on the left. You might have a bad bulb socket. I'm sure you can find a good used replacement assembly somewhere.
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I plugged the left into the right and it worked on the good side. I also tried jumping the wire from the brake switch at the peddle directly to the wire for the tail light and that allows the brake light to work but doesn't allow the turn signals to work then.
Laughing Gas
Joined: Dec 2010
Posts: 1,091
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From: Tucson, Arizona
I believe it's most likely the brake light switch that screws into your master cylinder. You obviously don't have any wiring or bulb issues. I would replace the brake switch before messing with the turn signal switch as it's easier to do and less expensive. You could try cleaning out the old one, but there's no guarantee that will fix it or that it will stay fixed. What condition is your brake fluid in? As that activates the switch, if it's ugly you might want to replace it.
Elder User
Joined: Aug 2004
Posts: 602
Likes: 1
From: Sacramento, CA.
I believe it's most likely the brake light switch that screws into your master cylinder. You obviously don't have any wiring or bulb issues. I would replace the brake switch before messing with the turn signal switch as it's easier to do and less expensive. You could try cleaning out the old one, but there's no guarantee that will fix it or that it will stay fixed. What condition is your brake fluid in? As that activates the switch, if it's ugly you might want to replace it.
Laughing Gas
Joined: Dec 2010
Posts: 1,091
Likes: 14
From: Tucson, Arizona
I can just tell you from my own personal experience that the brake light switch may be the culprit. In my case, one brake light would function intermittently. I installed a new switch and the malfunction was cured. If his rear turn signals both work, the wiring and bulbs are both OK as the brake lights share the same wiring and bulb filaments. He's already replaced the flasher, which shouldn't affect his brake lights anyway, other than one of the brake switch wires (the red one) plugs into it, and then goes on to the fuse box. That leaves the brake switch or the turn signal switch. The brake switch is cheaper and easier to change out than the T/S switch so if it were me, I'd try that one first.
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Cargo Master
Joined: Apr 2003
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An easy way to eliminate the brake switch is to run a jumper wire between both wires. If the problem still exists, it's not the switch. If the problem is fixed, it could be the switch.
Since one brake light and both turn signals works, I also don't think it is the brake switch and that it is a bad connection within the turn signal switch.
If I'm not mistaken, there is not a switch near the pedal if it is stock. Custom work or the work of a previous owner could complicate trouble shooting, in which case none of us can really be much help. You just need to figure out what was done and then formulate a plan to fix it.
Since one brake light and both turn signals works, I also don't think it is the brake switch and that it is a bad connection within the turn signal switch.
If I'm not mistaken, there is not a switch near the pedal if it is stock. Custom work or the work of a previous owner could complicate trouble shooting, in which case none of us can really be much help. You just need to figure out what was done and then formulate a plan to fix it.
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