I purchased a LED light from eBay, and hooked it up to my brake lights.
The light goes at the bottom of the rear bumper and it's supposed to flash 3 times when you tap the brake. It stay steady (on) when the headlights are switched on.

Whenever I drive my car with the headlights on, the VSA light comes on after driving for about 5 miles. This only happens when the headlights are on. After the VSA light comes on, the rear end actually feels very light. I'm scared to take a curve too fast, as I might lose control of the car.

I can drive in the day time, no headlights, and this problem never happens.

What could be the problem?

Below are pictures of what the light looks like and the VSA sign.

Please help.