To replace the electric antenna mast on a 1999 Shogun 2.8TDI, first, ensure the vehicle is turned off and the radio is disconnected. Carefully remove the interior trim panel surrounding the antenna base to access the motor. Disconnect the antenna wiring and remove the old mast by unscrewing or pulling it out, then insert the new mast and reassemble everything in reverse order. Finally, reconnect the radio and test the new antenna to ensure it operates correctly.