I installed a LED brake light to my 94 accord and and now the dashboard brake light stays lit. I did not remove any of the original bulbs or wiring. The LED power was taken from splicing into the third backup light wiring. I am not sure how the ECU triggers this warning light. Does it measure a current range?

 

You might be pulling just enough more amps to cause that to happen. As the sensor is looking for a certain draw to keep the light off.