i had that problem on my old 90..
Just had a bunch of wires stuck on the dash.. all i did was buy a stereo, usually they come with a connector with all the naked wires out the back.. just matched em up to the ones hanging about on the dash..
just tested different combinations of wires, always remember to earth one to the bodywork..
i know thats not much help.. but ye just try different combinations.. i got there in the end and i know nothing about electrics..
as for the interior light, i found only needed an earth wire and a live wire, no ignition wire was needed.. so if you find the right ones, just attach some longer (correct thickness) wires to them, run them through the dash up the side of windscreen and across underneath the headlining..
Piece of ****... (he says!!)