My Ranger's third brake light stays on when I have the parking lamps on. it does get brighter when I step on the brake and it does not blink when the turn signal is on. I do have after market LED tail lights and the third brake light is aftermarket LED as well. It just started recently and have not changed anything. Thanks in advance.

 

Sounds like the tail lights may be the problem, passing current through the running lights to the brake. Depending on how much is leaking, you may be able to correct the issue with a load resistor.