The 1a and 1b have different behaviour due to the 1b having dim/dip
1a
1st click sidelights only, headlights stay off and down
2nd click sidelights on, headlights up and on
1b
1st click sidelights on, headlights up and on dim/dip
2nd click sidelights and headlights up and on normal
There are 2 articles in KY2 on how to modify this behaviour.
FYI
Dim-Dip Lamps (UK Only)
UK regulations briefly required vehicles first used on or after 1 April 1987 to be equipped with a dim-dip device[17] or special running lamps, except such vehicles as comply fully with ECE Regulation 48 regarding installation of lighting equipment. A dim-dip device operates the low beam headlamps (called "dipped beam" in the UK) at between 10% and 20% of normal low-beam intensity. The running lamps permitted as an alternative to dim-dip were required to emit at least 200 candelas straight ahead, and no more than 800 candelas in any direction. In practise, most vehicles were equipped with the dim-dip option rather than the running lamps.
The dim-dip systems were not intended for daytime use as DRLs. Rather, they operated if the engine was running and the driver switched on the parking lamps (called "sidelights" in the UK). Dim-dip was intended to provide a nighttime "town beam" with intensity between that of parking lamps (commonly used by British drivers in city traffic after dark) and dipped/low beams, because the former were considered insufficiently intense to provide improved conspicuity in conditions requiring it, while the latter were considered too glaring for safe use in built-up areas. The UK was the only country to use such dim-dip systems.[18]
In 1988, the European Commission successfully prosecuted the UK government in the European Court of Justice, arguing that the UK requirement for dim-dip was illegal under EC directives prohibiting member states from enacting vehicle lighting requirements not contained in pan-European EC directives. As a result, the UK requirement for dim-dip was quashed. Nevertheless, dim-dip was (and is) still permitted, and while such systems are not presently as common as they once were, dim-dip functionality was fitted on many new cars well into the 1990s.
Think I'll ave a go at it this wkend tho & see if I can do it, just been reading the article in the Know Ur 2 section & it looks pretty straight forward 
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