Garmin makes an "integrated" FM traffic info receiver for some models of GPS that allows connection to the car's AM/FM antenna. But not my model (Nuvi660); I must use only the GTM20, a cigarette-lighter-powered model:
Benefits of using the car's antenna are mostly stealth: the cord-that-is-the-antenna between the cigarette lighter (which will be relocated inside the glove box) and the GPS plug that lays on the dashboard makes for an advertisement to crooks. And the car's antenna would, arguably, work better.
What are my options re. adapting the GTM20 to work with the car's antenna? Could this be as simple as splicing in a motorola antenna plug to the cable? Or...?