Installed LED's in my car...but even when "off" they stay dimly lit.

[BrianG]

It could be a number of things really.

Chances are the circuit needs a certain load to function correctly. You could add a resistor in parallel with the LED set to draw more current, but it would just make heat for nothing. There are other ways to get around this, but would need to study the circuit (voltages during the on and off states, at the stock current draw) to come up with a solution.