The woman wearing the strap-on stands while the other partner sits on the hood of the car. The seated partner may need to brace her feet on the bumper and scootch her butt forward a bit to get in position to receive the cock. The standing partner can lean forward on the hood of the car or grasp her partner's butt or waist. Let the car cool off a bit if you need to, so you don't burn your buns.