Pre-record the audio portions of the scene, especially if the car is to be moving in the scene.
Buy compact lighting equipment (fluorescent tubes) and cameras. Shop for used gear on online auction sites. Search through video production stores if you live in cities like Los Angeles, New York or Miami where shooting video on location is common. In the book "No-Budget Digital Filmmaking: How to Create Professional-Looking Videos for Little or No Cash," Chuck B. Gloman writes, "Use your power in video for good. If you need anything for a no-budget video shoot, ask around to see if you can get it for no cost."
Mount the lights and camera to a secure area within the car for establishing shots. Shoot a few shots from the exterior of the car through the windshield and side windows.
Place a board on the shoulders of the passenger's and driver's seat. Place the camera on top. Seat the actors next to each other in the back seat and record the lines.
Mount the camera on the dashboard or the rearview mirror for scenes that take place in the front of the car.
Record the actors one by one for close-up shots. Position the camera on the cameraman's steady shoulder. Sit the cameraman inside the car with the speaking subject. Record each subject's close-ups.
Apply for your film permit before shooting any scenes. Applications are accepted by your state's film commission. Pay an application processing fee of $150 or more depending on location. An insurance policy of $1 million is often required to begin shooting.
Buy a hood mount kit. Kits can cost from $200 to $1000. Find a retail resource by reviewing publications like Variety, DV Magazine and Hollywood Reporter.
Choose overcast days for your car scene to minimize the impact of natural light. Beware of glare from the windows when lighting your scenes.
Mount camera and lighting equipment to the window of the car, leaving the battery off. Bill Farnsworth, a television cameraman, writes for Video University, "The foremost important thing to have is redundant safety features. Or, make sure all the gear is strapped and clamped down tightly."
Perform a test run to make sure the angles the camera has been set up for and the lighting through the window work perfectly for the effect that you are trying to get.
Adjust the lighting to the natural light available. In the book "Lighting for Digital Video and Television" John Jackman writes, "Close-ups where eyes and expressions need to be visible can be effectively lit with a careful combination of moonlight and instrument panel." Then, shoot the live-action scene.