Cool web site and a LED issue.

First go to this web sit and move your arrow around.
Cool, huh?
Sorry, I've just never seen that before.
Playing with LEDs is new to me.
Why do we need resistors in led

This post could go under brakes but since it's an electrical thing.
Anyone had this issue?
I replaced the brake warning light with an LED.
After driving the car with a complete, new brake system the LED started coming on.
The warning switch now has about 3.5K resistance to ground and that is lighting up the LED.
It does not light up an incandescent light.
I'm using a combination valve that I rebuilt I'm wondering what is going on with the valve.
Here. Pretty simple.
1970 - 1976 Mopar Combination Valve Rebuild | Muscle Car Research LLC
Brake action is fine.

Tomorrow I will wack the valve to see if the piston is stuck and almost making contact with the switch.
But if noting changes, I'm thinking I'll add a resistor to the switch wire to make more resistance.
Think that will work?

I'm thinking the switch will still function and the LED will come on as long as the resistor isn't over 3.5K.
(Of course I could just use an incandescent bulb. But the LED is cool.)