If it is the bog standard AM/FM radio, just buy a cheap screen mounted aerial, hang it on the passenger seat or place it on the top of the dash, remove the radio, unplug the existing aerial and plug in the cheap test aerial.
That was what I did when I swopped my AM/FM radio for an AM/DAB equivalent one, really so that I could find out if the used radio worked okay quickly, before going to the bother of fitting an extra booster and cable.
Edit:- was it an "AA" booster that you removed?