My car is completely positive?

The positive current from my battery flows through my car all the way back to the ground on the battery. I put a tester light on the negative cable and got power using the battery post as a ground. there is no other ground on the car current is flowing through the entire metal parts of the car. when I turn the key nothing happens except the test light becomes brighter when I touch it to any metal piece on the car, engine, frame, relays, etc.