‘Right’ and ‘left’ low beam are separately fused, Bob - as are ‘right’ and ‘left’ high.
Typical fuse problem - replace ‘right’ low beam fuse as first step - cleaning connectors as per MRCHB . If that doesn’t fix the problem - some work with a multimeter at various places may be required…
Incidentally, ‘light comes on’ when switched to high beam is the separate high beam filament in the outer bulb - the low beam filament is not powered in ‘high’ beam…
xj6 85 Sov Europe (UK/NZ)