From ex Auto sparks....now retired...you may not have a fault !!.......back in the early days 80s...into 90s...the law required Head lamps to come on be it half brightness as soon as ignition on engine running and side lights on [ only note ] known as the "Dim-dip system" ...both head lamps come on ...on at half power...all fords.... British leyland....GM vauxhals etc etc had the system as standard...so to re-cap....NO ignition on...switch side lights on...then you see just small side lights on.....now turn ignition on....both head lamps come on , all be it not full brightness...OK...thats correct to your S2 car...then turning the head lights on normal full power ie...main & dip beams full power....the "Dim-dip system" is then by-passed.....if your car is in any way different to above then there is a fault.... hope of help...Peter.