Taillights Always On

[Dadeo]

My LED taillights are always on, but the license plate light is off. When I turn the parking lights on, the license plate light comes on with all 4 parking lights. Brake lights and turn signal lights work fine. Why are my taillights always on?

 

[Mach1 Driver]

The question is too general, we need more information- what year car? Whose LED lights- brand, type, etc. Which lights are always on? There are two types of lights, the brighter brake/turn, or lower intensity park/on, which is always on?
If its the brakes, it could be the brake light switch. It is important to know the year because there are different types of brake switches- some are pedal operated, and some are pressure actuated. Did this just start happening, or did it happen when you installed the LEDs?

 

[Dadeo]

1967 GT Fastback, generic bayonet LED incandescent replacement bulbs, only rear parking lights are on all the time, low intensity.
Pedal operated brake lights and turn signal lights work as they should. (not an issue)
This problem just happened recently, otherwise it all worked fine for the past 10 years.

 

[Mach1 Driver]

My first inclination is to treat it as though it is an incandescent light, and check the grounds to the tail lights- at each socket and the common ground which is a ring terminal screwed to the trunk latch support. Clean them all up and make sure they are tight. Also check the inside of the sockets for corrosion. Don't forget to check the license plate light, as it is on the same circuit.
If that doesn't do I would temporarily disconnect the wire going to light switch terminal P and see if it goes away- if so its the light switch.
Let us know how you make out, an LED only takes about 1/10th the power to operate and sometimes can be real head scratchers.
Wire 14 is black and goes to terminal P:

 

[Dadeo]

Thanks for your help. It's either the light switch or the fog light switch.

 

[Mach1 Driver]

Thanks for your help. It's either the light switch or the fog light switch.

I don't see how it could be the fog light switch- there is no relation in the circuits. Do yourself a favor and test by disconnecting the wire shown above, before you start replacing parts.

 

[Midlife]

I don't see how it could be the fog light switch- there is no relation in the circuits. Do yourself a favor and test by disconnecting the wire shown above, before you start replacing parts.

That's incorrect, as when the foglamps are on, so are the running lights. The connection to the running lights is by the female bullet as indicated above.
To test the foglamp switch, disconnect the 3 pin plug to the switch itself. If no change, then unplug the headlight switch.
The presence of the LED's are a red herring; without the key in ACC or RUN, there's no power to the running lights.

Now then, I wonder if the OP is confusing the brake lights with the running lights; he says no...

 

[Mach1 Driver]

That's incorrect, as when the foglamps are on, so are the running lights.

Ahhh, ok, you would know Mid. I don't have a wire diagram for a 67. I thought it was a stand-alone switch with no connection, but they get power from the light switch. But if it has a separate Frog switch its unlikely to be the culprit. Anyway, Dadeo, try disconnecting the wire to see if it goes away.

 

[Dadeo]

Thanks for all of your input. I'll certainly follow your suggestions when weather permits.
As the original owner, I decided to rebuild it in a single car garage with the help of my wife and these old bones don't allow for contortions under the dash in such a confined space. I'll be sure to post the results when I complete the repair.
Thanks again and Happy New Year to all!