The "Shift Light " as you call it would appear to be very much an item fitted to rally or race cars and to my knowledge there are no members heavily involved in such sports.
I would think you may have better success in contacting a forum dedicated to motor sports or even contact someone who actually participates in rallying or such.
As a matter iof interest did the "light" not come with fitting instructions - if not you could try doing a websearch for instructions
The problem is not so technical, basically what a shiftlight or tach need to work is just 2 things, current and a pulse.
The pulse cars emit varies depending on the number of cylinders, most tachs/shiftlights have 3 options for 8,6,4 cylinders.
Most of the time the pulse is gotten from the
and you clip wires depending on how many cylinders it has.
Some times you need an adapter because the ignition system uses a double spark system that gives pulses like it were a 2 cylinder car, so you have to buy the adapter.
However, on the Clio we got current (shiftlight starts when i open the switch) but we have no pulse it seems so i am unsure how the ignition system of the Clio works, why cant i get negative pulses?
BTW the shiftlight is like this one: http://www.summitracing.com/parts/SUM-G2945/
(not sure if exact model but very alike)