When I work on a radio, I always power it with my trickle battery charger. That way everything is fully protected. I never use a truck battery to do that.
For the antenna, you can use a piece of hookup wire. Just bare about 1/2" and poke it into the center hole in the socket. If it touches the casing, it will short out the signal.
The radio is probably all or part solid state. Make sure that you have the speaker connected and start out at low volume. It may not be too tolerant of being run without a speaker.
