how do i find out which wires go were on my c15 van for stereo?

can anybody help,purchased a c15 van,theres no stereo in it,so ive got my own jvc,problem is.theres no normal.red pos,black neg,yellow constant,theres to blocks with the wires on,so i pluged them straight to new head unit via jvc block,which do fit.but nothing,the citreon wires are pink,white,yellowgreen,and green,am totaly baffled by it,can anybody help,thanks pete..