For the most part, any shielded wire will recieve the signal. Based on the age of your vehicle, I'd say you have a mono based system. Even if you have a stereo system, theoretically, you can still use something as simple as a length of coaxial cable as an antenna. (I know coax. works with home stereo equipment as I've done it several times before.) You could simply relocate the exposed end of the antenna to inisde of the passanger area of the car, and solder/wire the other end into the reciever for the head unit. Just have to make sure you relocate the open end of the cable to an area not likely to see high EM radiation.