I have this light too and have been wondering what it it. It is a little green light on a little black box (about 1in wide x 2in long). There is a switch on the back of the box. If you flip the switch up, the green light blinks. If you flip the switch down, the light just remains on. I tried starting my car with both ways and it starts, so it is not a kill switch. The only thing attached to the black box is one chord that almost feels like a power cord.

The only thing I can think it might be is just a dummy alarm, so that it looks like another alarm system or something? That cord just hooks it up to power and thats it?

I'll try to remember to take a pic of it sometime.

 

Wiper Handle broke+hanging by wires-wont shut off.Windshield giant spider CRACKED. Just saw a green blinking light, hanging from wires +old tape -between brake pedal+Em pedal-Panic-after the key didnt turn+steering wheel was locked in place.Its ok now.WHAT IS THE LIGHT?

 

Follow the wires and see where it goes.