Went thru this on my '73. Soon enough, the wire became disconnected from the window, so I gave up.

Normally, an antenna has two conductors - the antenna itself, and a ground. Since the glass can't be grounded, the glass style of antenna just gives you the antenna, and the ground comes from grounding the radio.

Now if you look at the wire, you notice it has one pin. if you look at the antenna connector of your radio, it has what is commonly known as a Motorola Jack. But the hole for the center pin is the same size as the pin in your windshield antenna.

SO, just buy a standard antenna extension (Mororola plug male-to-female). 18" ought to do it, 2' will be plenty. Shove the windshield connector way down into the female. the single pin will fit right in the center pin hole of the Motorola jack. Tape it up so it won't come apart. Plug the other end of the extension into the radio.

Make awful darn sure that the wire off the windshield (and the extension) can't get caught up in the wiper linkage, or it's all for naught!