The 1999 Nissan Altima was sold with either a retractable power antenna or a fixed mast antenna. Both of these antennas are located on the passenger side rear fender. The antenna components are attached to the inside passenger sidewall of the trunk. Both types of antennas connect to the radio via a coaxial cable. Replacing either the fixed antenna or the retractable antenna mast is a straightforward job that requires only a small crescent wrench.
Remove the mast from the rear fender. You will need to turn the mast counterclockwise with your hands.
Open the trunk and locate the antenna components on the right side, or passenger side, trunk wall.
Unscrew the nut that attaches the antenna base to the trunk wall, with a crescent wrench, and remove the base.
Disconnect the coaxial antenna cable by turning its nut counterclockwise with the wrench.
Remove the mounting bolt and detach the antenna.
Install the new antenna by following the reverse order.
Open the trunk and locate the antenna components on the right trunk wall.
Use a crescent wrench to remove the antenna nut and antenna base.
Power on the radio to raise the mast. As the mast rises, pull it out of its housing. Notice which way the teeth are facing on the plastic gear in the antenna tube housing.
Make sure your new antenna rod is fully retracted before installing it.
Feed the new plastic antenna rod gear into the antenna tube, making sure its teeth match the gear in the antenna tube housing. Also make sure the radio is still on when you do this. When you have fed the plastic gear as far into the tube as it will go, power off the radio. As the gear retracts, guide the antenna mast into place. If the mast doesn't fully retract, repeat the removal and installation procedure. You must ensure the gear is in as far as possible before you turn off the radio.
Replace the antenna base and antenna nut, using the crescent wrench.
