J-4104, 1985.
The aircraft is fitted with a Northrop ALQ-171 ECM (Electronic Counter Measures) pod, in a publicity photograph for Northrop.
The equipment was intended for the Swiss Air Force Northrop F5E Tiger, but after disappointing tests the procurement was cancelled in 1989.

© Schweizer Flugwaffe, from  ein jäger für die schweiz (Borgeaud/Gunti/Lewis)