There are two types of antennae used on Isuzu vehicles. The first type is mounted on the body. To remove/install this type, simply disconnect the antenna lead wire from the radio, remove the mounting screw and remove the antenna from the body panel.
The second type is mounted in the windshield and only the antenna cable may be serviced.
Once the new antenna is installed, the radio must be trimmed. The trim adjustment is located on the back panel of the radio. Set the radio to a weak AM station around 1400 on the dial. Use a trim adjusting tool to fine tune the radio for the best reception.