1. Hold any color of Chemlight in your hand.
2. "Turn-On/Crack" the Chemlight.
2. Get into any vehicle, while still holding the chemlight in your hand, doesn't matter what seat.
Don't think the vehicle matters, I've been able to reproduce it in Helicopters and Vanilla Cars.
3. Get out of the vehicle, you'll notice the chemlight is turned off and allows you to "Turn-On/Crack" it again.