Service lamps/parking lights work but when I turn on the headlamps only high beam seams to work. Having replaced the headlamp model and what I thought was the 7.5 amp fuses for the low/ high beam they still don't work. Need more help trouble shooting. Thanks...

1994 XJS V12 Convertible.

 

Pardon the dumb question, but have you checked the bulbs? There are two filaments in each bulb, high beam and low beam.