To bench test, connect an antenna, speaker, and power to two +14V terminals. An original connector with a few inches of pigtail will make it easier to connect power from 12 volt source. If you don't have one, make sure your 12 volt source connects to both + 14 volt terminals.
For the ground from power source I attached alligator clips to one of the small 1/4" hex head body screws.
For the speaker you will want to use a 10 or 8 ohm speaker (modern 4 ohm speakers and overload the radio). If you have an original working speaker, or at least the original connector and some pigtail, it makes testing easier. Test all the control functions and be sure and check am and fm.
For the antenna function, attach multi tester to the green and white wire (our outer antenna connector) and push in on the right side radio knob. This sends voltage to antenna motor to push it out. Your voltage reading should go from zero to 10 or more volts with ground on the antenna connector at radio. Next attach tester to blue and white wire (inner antenna connector) and pull on the knob which retracts antenna and you should get 10 or more volts.
That's it. As you see, in video even with this old original speaker it still sounds pretty good.