There is a hole on the kick panel, above the cowl vents, where the coaxial cable passes through to the cowl drain area then up to the base of the antenna. If you peek under the passenger side dash you should see the coax or the empty hole. It is common for the original crimped cable connection at the antenna base to rust/corrode and fall off.
Now, the bad news; In order to access the cowl drain area, you have to remove the cowl vent housing. The were installed with a heavy caulk and can be a real pain to remove.
The photo below shows the view of the cowl drain area looking through the antenna hole.
And the next shot taken from the vent opening shows the coax cable where it exits the kick panel and goes up to the antenna.